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  • 1.
    Abdulla, Parosh Aziz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Atig, Mohamed Faouzi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Leonardsson, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ros, Alberto
    Zhu, Yunyun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Fencing programs with self-invalidation and self-downgrade2016In: Formal Techniques for Distributed Objects, Components, and Systems, Springer, 2016, p. 19-35Conference paper (Refereed)
  • 2.
    Abdulla, Parosh Aziz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Atig, Mohamed Faouzi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Leonardsson, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ros, Alberto
    Zhu, Yunyun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Mending fences with self-invalidation and self-downgrade2018In: Logical Methods in Computer Science, ISSN 1860-5974, E-ISSN 1860-5974, Vol. 14, no 1, article id 6Article in journal (Refereed)
  • 3.
    Alipour, Mehdi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Carlson, Trevor E.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Maximizing limited resources: A limit-based study and taxonomy of out-of-order commit2019In: Journal of Signal Processing Systems, ISSN 1939-8018, E-ISSN 1939-8115, Vol. 91, no 3-4, p. 379-397Article in journal (Refereed)
    Abstract [en]

    Out-of-order execution is essential for high performance, general-purpose computation, as it can find and execute useful work instead of stalling. However, it is typically limited by the requirement of visibly sequential, atomic instruction executionin other words, in-order instruction commit. While in-order commit has a number of advantages, such as providing precise interrupts and avoiding complications with the memory consistency model, it requires the core to hold on to resources (reorder buffer entries, load/store queue entries, physical registers) until they are released in program order. In contrast, out-of-order commit can release some resources much earlier, yielding improved performance and/or lower resource requirements. Non-speculative out-of-order commit is limited in terms of correctness by the conditions described in the work of Bell and Lipasti (2004). In this paper we revisit out-of-order commit by examining the potential performance benefits of lifting these conditions one by one and in combination, for both non-speculative and speculative out-of-order commit. While correctly handling recovery for all out-of-order commit conditions currently requires complex tracking and expensive checkpointing, this work aims to demonstrate the potential for selective, speculative out-of-order commit using an oracle implementation without speculative rollback costs. Through this analysis of the potential of out-of-order commit, we learn that: a) there is significant untapped potential for aggressive variants of out-of-order commit; b) it is important to optimize the out-of-order commit depth for a balanced design, as smaller cores benefit from reduced depth while larger cores continue to benefit from deeper designs; c) the focus on implementing only a subset of the out-of-order commit conditions could lead to efficient implementations; d) the benefits of out-of-order commit increases with higher memory latency and in conjunction with prefetching; e) out-of-order commit exposes additional parallelism in the memory hierarchy.

  • 4.
    Alipour, Mehdi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Carlson, Trevor E.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Exploring the performance limits of out-of-order commit2017In: Proc. 14th Computing Frontiers Conference, New York: ACM Press, 2017, p. 211-220Conference paper (Refereed)
  • 5.
    Alirezaie, Marjan
    et al.
    Örebro University.
    Renoux, Jennifer
    Örebro University.
    Köckemann, Uwe
    Örebro University.
    Kristoffersson, Annica
    Örebro University.
    Karlsson, Lars
    Örebro University.
    Blomqvist, Eva
    SICS East.
    Tsiftes, Nicolas
    SICS.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. SICS.
    Loutfi, Amy
    Örebro University.
    An Ontology-based Context-aware System for Smart Homes: E-care@ home2017In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 17, no 7Article in journal (Refereed)
  • 6. Alonso, Juan M.
    et al.
    Nordhamn, Amanda
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Olofsson, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Bounds on the lifetime of wireless sensor networks with lossy links and directional antennas2016In: Wireless Network Performance Enhancement via Directional Antennas: Models, Protocols, and Systems, Boca Raton, FL: CRC Press, 2016, p. 329-361Chapter in book (Refereed)
  • 7.
    Alves, Ricardo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Leveraging Existing Microarchitectural Structures to Improve First-Level Caching Efficiency2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Low-latency data access is essential for performance. To achieve this, processors use fast first-level caches combined with out-of-order execution, to decrease and hide memory access latency respectively. While these approaches are effective for performance, they cost significant energy, leading to the development of many techniques that require designers to trade-off performance and efficiency.

    Way-prediction and filter caches are two of the most common strategies for improving first-level cache energy efficiency while still minimizing latency. They both have compromises as way-prediction trades off some latency for better energy efficiency, while filter caches trade off some energy efficiency for lower latency. However, these strategies are not mutually exclusive. By borrowing elements from both, and taking into account SRAM memory layout limitations, we proposed a novel MRU-L0 cache that mitigates many of their shortcomings while preserving their benefits. Moreover, while first-level caches are tightly integrated into the cpu pipeline, existing work on these techniques largely ignores the impact they have on instruction scheduling. We show that the variable hit latency introduced by way-misspredictions causes instruction replays of load dependent instruction chains, which hurts performance and efficiency. We study this effect and propose a variable latency cache-hit instruction scheduler, that identifies potential misschedulings, reduces instruction replays, reduces negative performance impact, and further improves cache energy efficiency.

    Modern pipelines also employ sophisticated execution strategies to hide memory latency and improve performance. While their primary use is for performance and correctness, they require intermediate storage that can be used as a cache as well. In this work we demonstrate how the store-buffer, paired with the memory dependency predictor, can be used to efficiently cache dirty data; and how the physical register file, paired with a value predictor, can be used to efficiently cache clean data. These strategies not only improve both performance and energy, but do so with no additional storage and minimal additional complexity, since they recycle existing cpu structures to detect reuse, memory ordering violations, and misspeculations.

    List of papers
    1. Addressing energy challenges in filter caches
    Open this publication in new window or tab >>Addressing energy challenges in filter caches
    2017 (English)In: Proc. 29th International Symposium on Computer Architecture and High Performance Computing, IEEE Computer Society, 2017, p. 49-56Conference paper, Published paper (Refereed)
    Abstract [en]

    Filter caches and way-predictors are common approaches to improve the efficiency and/or performance of first-level caches. Filter caches use a small L0 to provide more efficient and faster access to a small subset of the data, and work well for programs with high locality. Way-predictors improve efficiency by accessing only the way predicted, which alleviates the need to read all ways in parallel without increasing latency, but hurts performance due to mispredictions.In this work we examine how SRAM layout constraints (h-trees and data mapping inside the cache) affect way-predictors and filter caches. We show that accessing the smaller L0 array can be significantly more energy efficient than attempting to read fewer ways from a larger L1 cache; and that the main source of energy inefficiency in filter caches comes from L0 and L1 misses. We propose a filter cache optimization that shares the tag array between the L0 and the L1, which incurs the overhead of reading the larger tag array on every access, but in return allows us to directly access the correct L1 way on each L0 miss. This optimization does not add any extra latency and counter-intuitively, improves the filter caches overall energy efficiency beyond that of the way-predictor.By combining the low power benefits of a physically smaller L0 with the reduction in miss energy by reading L1 tags upfront in parallel with L0 data, we show that the optimized filter cache reduces the dynamic cache energy compared to a traditional filter cache by 26% while providing the same performance advantage. Compared to a way-predictor, the optimized cache improves performance by 6% and energy by 2%.

    Place, publisher, year, edition, pages
    IEEE Computer Society, 2017
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-334221 (URN)10.1109/SBAC-PAD.2017.14 (DOI)000426895600007 ()978-1-5090-1233-6 (ISBN)
    Conference
    29th International Symposium on Computer Architecture and High Performance Computing SBAC-PAD, 2017, October 17–20, Campinas, Brazil.
    Available from: 2017-11-09 Created: 2017-11-21 Last updated: 2019-05-22Bibliographically approved
    2. Dynamically Disabling Way-prediction to Reduce Instruction Replay
    Open this publication in new window or tab >>Dynamically Disabling Way-prediction to Reduce Instruction Replay
    2018 (English)In: 2018 IEEE 36th International Conference on Computer Design (ICCD), IEEE, 2018, p. 140-143Conference paper, Published paper (Refereed)
    Abstract [en]

    Way-predictors have long been used to reduce dynamic cache energy without the performance loss of serial caches. However, they produce variable-latency hits, as incorrect predictions increase load-to-use latency. While the performance impact of these extra cycles has been well-studied, the need to replay subsequent instructions in the pipeline due to the load latency increase has been ignored. In this work we show that way-predictors pay a significant performance penalty beyond previously studied effects due to instruction replays caused by mispredictions. To address this, we propose a solution that learns the confidence of the way prediction and dynamically disables it when it is likely to mispredict and cause replays. This allows us to reduce cache latency (when we can trust the way-prediction) while still avoiding the need to replay instructions in the pipeline (by avoiding way-mispredictions). Standard way-predictors degrade IPC by 6.9% vs. a parallel cache due to 10% of the instructions being replayed (worst case 42.3%). While our solution decreases way-prediction accuracy by turning off the way-predictor in some cases when it would have been correct, it delivers higher performance than a standard way-predictor. Our confidence-based way-predictor degrades IPC by only 4.4% by replaying just 5.6% of the instructions (worse case 16.3%). This reduces the way-predictor cache energy overhead compared to serial access cache, from 8.5% to 3.7% on average and on the worst case, from 33.8% to 9.5%.

    Place, publisher, year, edition, pages
    IEEE, 2018
    Series
    Proceedings IEEE International Conference on Computer Design, ISSN 1063-6404, E-ISSN 2576-6996
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-361215 (URN)10.1109/ICCD.2018.00029 (DOI)000458293200018 ()978-1-5386-8477-1 (ISBN)
    Conference
    IEEE 36th International Conference on Computer Design (ICCD), October 7–10, 2018, Orlando, FL, USA
    Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-05-22Bibliographically approved
    3. Minimizing Replay under Way-Prediction
    Open this publication in new window or tab >>Minimizing Replay under Way-Prediction
    2019 (English)Report (Other academic)
    Abstract [en]

    Way-predictors are effective at reducing dynamic cache energy by reducing the number of ways accessed, but introduce additional latency for incorrect way-predictions. While previous work has studied the impact of the increased latency for incorrect way-predictions, we show that the latency variability has a far greater effect as it forces replay of in-flight instructions on an incorrect way-prediction. To address the problem, we propose a solution that learns the confidence of the way-prediction and dynamically disables it when it is likely to mispredict. We further improve this approach by biasing the confidence to reduce latency variability further at the cost of reduced way-predictions. Our results show that instruction replay in a way-predictor reduces IPC by 6.9% due to 10% of the instructions being replayed. Our confidence-based way-predictor degrades IPC by only 2.9% by replaying just 3.4% of the instructions, reducing way-predictor cache energy overhead (compared to serial access cache) from 8.5% to 1.9%.

    Series
    Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2019-003
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-383596 (URN)
    Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-07-03Bibliographically approved
    4. Filter caching for free: The untapped potential of the store-buffer
    Open this publication in new window or tab >>Filter caching for free: The untapped potential of the store-buffer
    2019 (English)In: Proc. 46th International Symposium on Computer Architecture, New York: ACM Press, 2019, p. 436-448Conference paper, Published paper (Refereed)
    Abstract [en]

    Modern processors contain store-buffers to allow stores to retire under a miss, thus hiding store-miss latency. The store-buffer needs to be large (for performance) and searched on every load (for correctness), thereby making it a costly structure in both area and energy. Yet on every load, the store-buffer is probed in parallel with the L1 and TLB, with no concern for the store-buffer's intrinsic hit rate or whether a store-buffer hit can be predicted to save energy by disabling the L1 and TLB probes.

    In this work we cache data that have been written back to memory in a unified store-queue/buffer/cache, and predict hits to avoid L1/TLB probes and save energy. By dynamically adjusting the allocation of entries between the store-queue/buffer/cache, we can achieve nearly optimal reuse, without causing stalls. We are able to do this efficiently and cheaply by recognizing key properties of stores: free caching (since they must be written into the store-buffer for correctness we need no additional data movement), cheap coherence (since we only need to track state changes of the local, dirty data in the store-buffer), and free and accurate hit prediction (since the memory dependence predictor already does this for scheduling).

    As a result, we are able to increase the store-buffer hit rate and reduce store-buffer/TLB/L1 dynamic energy by 11.8% (up to 26.4%) on SPEC2006 without hurting performance (average IPC improvements of 1.5%, up to 4.7%).The cost for these improvements is a 0.2% increase in L1 cache capacity (1 bit per line) and one additional tail pointer in the store-buffer.

    Place, publisher, year, edition, pages
    New York: ACM Press, 2019
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-383473 (URN)10.1145/3307650.3322269 (DOI)978-1-4503-6669-4 (ISBN)
    Conference
    ISCA 2019, June 22–26, Phoenix, AZ
    Funder
    Knut and Alice Wallenberg FoundationEU, Horizon 2020, 715283EU, Horizon 2020, 801051Swedish Foundation for Strategic Research , SM17-0064
    Available from: 2019-06-22 Created: 2019-05-16 Last updated: 2019-07-03Bibliographically approved
    5. Efficient temporal and spatial load to load forwarding
    Open this publication in new window or tab >>Efficient temporal and spatial load to load forwarding
    2020 (English)In: Proc. 26th International Symposium on High-Performance and Computer Architecture, IEEE Computer Society, 2020Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    IEEE Computer Society, 2020
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-383477 (URN)
    Conference
    HPCA 2020, February 22–26, San Diego, CA
    Note

    to appear

    Available from: 2019-08-21 Created: 2019-05-16 Last updated: 2019-08-21Bibliographically approved
  • 8.
    Alves, Ricardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Dynamically Disabling Way-prediction to Reduce Instruction Replay2018In: 2018 IEEE 36th International Conference on Computer Design (ICCD), IEEE, 2018, p. 140-143Conference paper (Refereed)
    Abstract [en]

    Way-predictors have long been used to reduce dynamic cache energy without the performance loss of serial caches. However, they produce variable-latency hits, as incorrect predictions increase load-to-use latency. While the performance impact of these extra cycles has been well-studied, the need to replay subsequent instructions in the pipeline due to the load latency increase has been ignored. In this work we show that way-predictors pay a significant performance penalty beyond previously studied effects due to instruction replays caused by mispredictions. To address this, we propose a solution that learns the confidence of the way prediction and dynamically disables it when it is likely to mispredict and cause replays. This allows us to reduce cache latency (when we can trust the way-prediction) while still avoiding the need to replay instructions in the pipeline (by avoiding way-mispredictions). Standard way-predictors degrade IPC by 6.9% vs. a parallel cache due to 10% of the instructions being replayed (worst case 42.3%). While our solution decreases way-prediction accuracy by turning off the way-predictor in some cases when it would have been correct, it delivers higher performance than a standard way-predictor. Our confidence-based way-predictor degrades IPC by only 4.4% by replaying just 5.6% of the instructions (worse case 16.3%). This reduces the way-predictor cache energy overhead compared to serial access cache, from 8.5% to 3.7% on average and on the worst case, from 33.8% to 9.5%.

  • 9.
    Alves, Ricardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Efficient temporal and spatial load to load forwarding2020In: Proc. 26th International Symposium on High-Performance and Computer Architecture, IEEE Computer Society, 2020Conference paper (Refereed)
  • 10.
    Alves, Ricardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Minimizing Replay under Way-Prediction2019Report (Other academic)
    Abstract [en]

    Way-predictors are effective at reducing dynamic cache energy by reducing the number of ways accessed, but introduce additional latency for incorrect way-predictions. While previous work has studied the impact of the increased latency for incorrect way-predictions, we show that the latency variability has a far greater effect as it forces replay of in-flight instructions on an incorrect way-prediction. To address the problem, we propose a solution that learns the confidence of the way-prediction and dynamically disables it when it is likely to mispredict. We further improve this approach by biasing the confidence to reduce latency variability further at the cost of reduced way-predictions. Our results show that instruction replay in a way-predictor reduces IPC by 6.9% due to 10% of the instructions being replayed. Our confidence-based way-predictor degrades IPC by only 2.9% by replaying just 3.4% of the instructions, reducing way-predictor cache energy overhead (compared to serial access cache) from 8.5% to 1.9%.

  • 11.
    Alves, Ricardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Nikoleris, Nikos
    ARM Res, Lund, Sweden.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Addressing energy challenges in filter caches2017In: Proc. 29th International Symposium on Computer Architecture and High Performance Computing, IEEE Computer Society, 2017, p. 49-56Conference paper (Refereed)
    Abstract [en]

    Filter caches and way-predictors are common approaches to improve the efficiency and/or performance of first-level caches. Filter caches use a small L0 to provide more efficient and faster access to a small subset of the data, and work well for programs with high locality. Way-predictors improve efficiency by accessing only the way predicted, which alleviates the need to read all ways in parallel without increasing latency, but hurts performance due to mispredictions.In this work we examine how SRAM layout constraints (h-trees and data mapping inside the cache) affect way-predictors and filter caches. We show that accessing the smaller L0 array can be significantly more energy efficient than attempting to read fewer ways from a larger L1 cache; and that the main source of energy inefficiency in filter caches comes from L0 and L1 misses. We propose a filter cache optimization that shares the tag array between the L0 and the L1, which incurs the overhead of reading the larger tag array on every access, but in return allows us to directly access the correct L1 way on each L0 miss. This optimization does not add any extra latency and counter-intuitively, improves the filter caches overall energy efficiency beyond that of the way-predictor.By combining the low power benefits of a physically smaller L0 with the reduction in miss energy by reading L1 tags upfront in parallel with L0 data, we show that the optimized filter cache reduces the dynamic cache energy compared to a traditional filter cache by 26% while providing the same performance advantage. Compared to a way-predictor, the optimized cache improves performance by 6% and energy by 2%.

  • 12.
    Alves, Ricardo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Ros, Alberto
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Filter caching for free: The untapped potential of the store-buffer2019In: Proc. 46th International Symposium on Computer Architecture, New York: ACM Press, 2019, p. 436-448Conference paper (Refereed)
    Abstract [en]

    Modern processors contain store-buffers to allow stores to retire under a miss, thus hiding store-miss latency. The store-buffer needs to be large (for performance) and searched on every load (for correctness), thereby making it a costly structure in both area and energy. Yet on every load, the store-buffer is probed in parallel with the L1 and TLB, with no concern for the store-buffer's intrinsic hit rate or whether a store-buffer hit can be predicted to save energy by disabling the L1 and TLB probes.

    In this work we cache data that have been written back to memory in a unified store-queue/buffer/cache, and predict hits to avoid L1/TLB probes and save energy. By dynamically adjusting the allocation of entries between the store-queue/buffer/cache, we can achieve nearly optimal reuse, without causing stalls. We are able to do this efficiently and cheaply by recognizing key properties of stores: free caching (since they must be written into the store-buffer for correctness we need no additional data movement), cheap coherence (since we only need to track state changes of the local, dirty data in the store-buffer), and free and accurate hit prediction (since the memory dependence predictor already does this for scheduling).

    As a result, we are able to increase the store-buffer hit rate and reduce store-buffer/TLB/L1 dynamic energy by 11.8% (up to 26.4%) on SPEC2006 without hurting performance (average IPC improvements of 1.5%, up to 4.7%).The cost for these improvements is a 0.2% increase in L1 cache capacity (1 bit per line) and one additional tail pointer in the store-buffer.

  • 13.
    Aris, Ahmet
    et al.
    Istanbul Technical University.
    Oktuğ, Sema
    Istanbul Technical University.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Security of Internet of Things for a Reliable Internet of Services2018In: Autonomous Control for a Reliable Internet of Services: Methods, Models, Approaches, Techniques, Algorithms, and Tools / [ed] Ivan Ganchev, R. D. van der Mei, Hans van den Berg, Cham , 2018Chapter in book (Refereed)
  • 14.
    Asan, Noor Badariah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Universiti Teknikal Malaysia Melaka, Melaka Malaysia.
    Carlos, Pérez Penichet
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Redzwan, Syaiful
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Noreland, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Hassan, Emadeldeen
    Umeå University.
    Rydberg, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Blokhuis, Taco
    Maastricht University Medical Center+, Netherlands.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Augustine, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Data Packet Transmission through Fat Tissue for Wireless Intra-Body Networks2017In: IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, ISSN 2469-7249Article in journal (Refereed)
    Abstract [en]

    This work explores high data rate microwave communication through fat tissue in order to address the wide bandwidth requirements of intra-body area networks. We have designed and carried out experiments on an IEEE 802.15.4 based WBAN prototype by measuring the performance of the fat tissue channel in terms of data packet reception with respect to tissue length and power transmission. This paper proposes and demonstrates a high data rate communication channel through fat tissue using phantom and ex-vivo environments. Here, we achieve a data packet reception of approximately 96 % in both environments. The results also show that the received signal strength drops by ~1 dBm per 10 mm in phantom and ~2 dBm per 10 mm in ex-vivo. The phantom and ex-vivo experimentations validated our approach for high data rate communication through fat tissue for intrabody network applications. The proposed method opens up new opportunities for further research in fat channel communication. This study will contribute to the successful development of high bandwidth wireless intra-body networks that support high data rate implanted, ingested, injected, or worn devices

  • 15.
    Asan, Noor Badariah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hassan, Emadeldeen
    Umea Univ, Dept Comp Sci, S-90187 Umea, Sweden;Menoufia Univ, Dept Elect & Elect Commun, Menoufia 32952, Egypt.
    Velander, Jacob
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Redzwan, Syaiful
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Noreland, Daniel
    Umea Univ, Dept Comp Sci, S-90187 Umea, Sweden.
    Blokhuis, Taco J.
    Maastricht Univ, Med Ctr, Dept Surg, NL-6229 HX Maastricht, Netherlands.
    Wadbro, Eddie
    Umea Univ, Dept Comp Sci, S-90187 Umea, Sweden.
    Berggren, Martin
    Umea Univ, Dept Comp Sci, S-90187 Umea, Sweden.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Augustine, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies2018In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 18, no 9, article id 2752Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the use of fat tissue as a communication channel between in-body, implanted devices at R-band frequencies (1.7-2.6 GHz). The proposed fat channel is based on an anatomical model of the human body. We propose a novel probe that is optimized to efficiently radiate the R-band frequencies into the fat tissue. We use our probe to evaluate the path loss of the fat channel by studying the channel transmission coefficient over the R-band frequencies. We conduct extensive simulation studies and validate our results by experimentation on phantom and ex-vivo porcine tissue, with good agreement between simulations and experiments. We demonstrate a performance comparison between the fat channel and similar waveguide structures. Our characterization of the fat channel reveals propagation path loss of similar to 0.7 dB and similar to 1.9 dB per cm for phantom and ex-vivo porcine tissue, respectively. These results demonstrate that fat tissue can be used as a communication channel for high data rate intra-body networks.

  • 16.
    Asan, Noor Badariah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Noreland, Daniel
    Hassan, Emadeldeen
    Redzwan, Syaiful
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rydberg, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Blokhuis, Taco J.
    Carlsson, Per-Ola
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Augustine, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Intra-body microwave communication through adipose tissue2017In: Healthcare Technology Letters, E-ISSN 2053-3713, Vol. 4, no 4, p. 115-121Article in journal (Refereed)
  • 17.
    Asan, Noor Badariah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Redzwan, Syaiful
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rydberg, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Augustine, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Noreland, Daniel
    Hassan, Emadeldeen
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Human fat tissue: A microwave communication channel2017In: Proc. 1st MTT-S International Microwave Bio Conference, IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, we present an approach for communication through human body tissue in the R-band frequency range. This study examines the ranges of microwave frequencies suitable for intra-body communication. The human body tissues are characterized with respect to their transmission properties using simulation modeling and phantom measurements. The variations in signal coupling with respect to different tissue thicknesses are studied. The simulation and phantom measurement results show that electromagnetic communication in the fat layer is viable with attenuation of approximately 2 dB per 20 mm. 

  • 18.
    Asan, Noor Badariah
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Velander, Jacob
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Redzwan, Syaiful
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Augustine, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hassan, Emadeldeen
    Department of Computing Science, Umeå University, Umeå, Sweden.
    Noreland, Daniel
    Department of Computing Science, Umeå University, Umeå, Sweden.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Blokhuis, Taco J.
    Department of Surgery, Maastricht University Medical Center+, Maastricht, The Netherland.
    Reliability of the fat tissue channel for intra-body microwave communication2017In: 2017 IEEE Conference on Antenna Measurements & Applications (CAMA), IEEE, 2017, p. 310-313Conference paper (Refereed)
    Abstract [en]

    Recently, the human fat tissue has been proposed as a microwave channel for intra-body sensor applications. In this work, we assess how disturbances can prevent reliable microwave propagation through the fat channel. Perturbants of different sizes are considered. The simulation and experimental results show that efficient communication through the fat channel is possible even in the presence of perturbants such as embedded muscle layers and blood vessels. We show that the communication channel is not affected by perturbants that are smaller than 15 mm cube.

  • 19.
    Bagci, Ibrahim Ethem
    et al.
    Univ Lancaster, Sch Comp & Commun, Lancaster, England.
    Raza, Shahid
    SICS Swedish ICT, Kista, Sweden.
    Roedig, Utz
    Univ Lancaster, Sch Comp & Commun, Lancaster, England.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. SICS Swedish ICT, Kista, Sweden.
    Fusion: Coalesced Confidential Storage and Communication Framework for the IoT2016In: Security and Communication Networks, ISSN 1939-0114, E-ISSN 1939-0122, Vol. 9, no 15, p. 2656-2673Article in journal (Refereed)
    Abstract [en]

    Comprehensive security mechanisms are required for a successful implementation of the Internet of Things (IoT). Existing solutions focus mainly on securing the communication links between Internet hosts and IoT devices. However, as most IoT devices nowadays provide vast amounts of flash storage space, it is as well required to consider storage security within a comprehensive security framework. Instead of developing independent security solutions for storage and communication, we propose Fusion, a framework that provides coalesced confidential storage and communication. Fusion uses existing secure communication protocols for the IoT such as Internet protocol security (IPsec) and datagram transport layer security (DTLS) and re-uses the defined communication security mechanisms within the storage component. Thus, trusted mechanisms developed for communication security are extended into the storage space. Notably, this mechanism allows us to transmit requested data directly from the file system without decrypting read data blocks and then re-encrypting these for transmission. Thus, Fusion provides benefits in terms of processing speed and energy efficiency, which are important aspects for resource-constrained IoT devices. This paper describes the Fusion architecture and its instantiation for IPsec-based and DTLS-based systems. We describe Fusion's implementation and evaluate its storage overheads, communication performance, and energy consumption.

  • 20. Baird, Ryan
    et al.
    Gavin, Peter
    Själander, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Whalley, David
    Uh, Gang-Ryung
    Optimizing transfers of control in the static pipeline architecture2015In: Proc. 16th ACM SIGPLAN/SIGBED Conference on Languages, Compilers, and Tools for Embedded Systems, New York: ACM Press, 2015, p. 7-16Conference paper (Refereed)
    Abstract [en]

    Statically pipelined processors offer a new way to improve the performance beyond that of a traditional in-order pipeline while simultaneously reducing energy usage by enabling the compiler to control more fine-grained details of the program execution. This paper describes how a compiler can exploit the features of the static pipeline architecture to apply optimizations on transfers of control that are not possible on a conventional architecture. The optimizations presented in this paper include hoisting the target address calculations for branches, jumps, and calls out of loops, performing branch chaining between calls and jumps, hoisting the setting of return addresses out of loops, and exploiting conditional calls and returns. The benefits of performing these transfer of control optimizations include a 6.8% reduction in execution time and a 3.6% decrease in estimated energy usage.

  • 21. Bardizbanyan, Alen
    et al.
    Själander, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Whalley, David
    Larsson-Edefors, Per
    Improving data access efficiency by using context-aware loads and stores2015In: Proc. 16th ACM SIGPLAN/SIGBED Conference on Languages, Compilers, and Tools for Embedded Systems, New York: ACM Press, 2015, p. 27-36Conference paper (Refereed)
    Abstract [en]

    Memory operations have a significant impact on both performance and energy usage even when an access hits in the level-one data cache (L1 DC). Load instructions in particular affect performance as they frequently result in stalls since the register to be loaded is often referenced before the data is available in the pipeline. L1 DC accesses also impact energy usage as they typically require significantly more energy than a register file access. Despite their impact on performance and energy usage, L1 DC accesses on most processors are performed in a general fashion without regard to the context in which the load or store operation is performed. We describe a set of techniques where the compiler enhances load and store instructions so that they can be executed with fewer stalls and/or enable the L1 DC to be accessed in a more energy-efficient manner. We show that using these techniques can simultaneously achieve a 6% gain in performance and a 43% reduction in L1 DC energy usage.

  • 22.
    Bor, Martin
    et al.
    Lancaster University.
    Roedig, Utz
    Lancaster University.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Alonso, Juan
    Univ. Nac. de Cuyo, Argentina.
    Do LoRa Low-Power Wide-Area Networks Scale?2016Conference paper (Refereed)
    Abstract [en]

    New Internet of Things (IoT) technologies such as LongRange (LoRa) are emerging which enable power ecientwireless communication over very long distances. Devicestypically communicate directly to a sink node which removesthe need of constructing and maintaining a complex multi-hop network. Given the fact that a wide area is coveredand that all devices communicate directly to a few sinknodes a large number of nodes have to share the commu-nication medium. LoRa provides for this reason a rangeof communication options (centre frequency, spreading fac-tor, bandwidth, coding rates) from which a transmitter canchoose. Many combination settings are orthogonal and pro-vide simultaneous collision free communications. Neverthe-less, there is a limit regarding the number of transmitters aLoRa system can support. In this paper we investigate thecapacity limits of LoRa networks. Using experiments wedevelop models describing LoRa communication behaviour.We use these models to parameterise a LoRa simulation tostudy scalability. Our experiments show that a typical smartcity deployment can support 120 nodes per 3.8 ha, which isnot sucient for future IoT deployments. LoRa networkscan scale quite well, however, if they use dynamic commu-nication parameter selection and/or multiple sinks.

  • 23.
    Borgström, Gustaf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Sembrant, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Adaptive cache warming for faster simulations2017In: Proc. 9th Workshop on Rapid Simulation and Performance Evaluation: Methods and Tools, New York: ACM Press, 2017, article id 1Conference paper (Refereed)
  • 24.
    Cambazoglu, Volkan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Protocol, mobility and adversary models for the verification of security2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing heterogeneity of communicating devices, ranging from resource constrained battery driven sensor nodes to multi-core processor computers, challenges protocol design. We examine security and privacy protocols with respect to exterior factors such as users, adversaries, and computing and communication resources; and also interior factors such as the operations, the interactions and the parameters of a protocol.

    Users and adversaries interact with security and privacy protocols, and even affect the outcome of the protocols. We propose user mobility and adversary models to examine how the location privacy of users is affected when they move relative to each other in specific patterns while adversaries with varying strengths try to identify the users based on their historical locations. The location privacy of the users are simulated with the support of the K-Anonymity protection mechanism, the Distortion-based metric, and our models of users' mobility patterns and adversaries' knowledge about users.

    Security and privacy protocols need to operate on various computing and communication resources. Some of these protocols can be adjusted for different situations by changing parameters. A common example is to use longer secret keys in encryption for stronger security. We experiment with the trade-off between the security and the performance of the Fiat–Shamir identification protocol. We pipeline the protocol to increase its utilisation as the communication delay outweighs the computation.

    A mathematical specification based on a formal method leads to a strong proof of security. We use three formal languages with their tool supports in order to model and verify the Secure Hierarchical In-Network Aggregation (SHIA) protocol for Wireless Sensor Networks (WSNs). The three formal languages specialise on cryptographic operations, distributed systems and mobile processes. Finding an appropriate level of abstraction to represent the essential features of the protocol in three formal languages was central.

    List of papers
    1. The impact of trace and adversary models on location privacy provided by K-anonymity
    Open this publication in new window or tab >>The impact of trace and adversary models on location privacy provided by K-anonymity
    2012 (English)In: Proc. 1st Workshop on Measurement, Privacy, and Mobility, New York: ACM Press, 2012, article id 6Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    New York: ACM Press, 2012
    National Category
    Computer Sciences
    Research subject
    Computer Science with specialization in Computer Communication
    Identifiers
    urn:nbn:se:uu:diva-171581 (URN)10.1145/2181196.2181202 (DOI)978-1-4503-1163-2 (ISBN)
    Conference
    MPM 2012
    Projects
    ProFuNWISENET
    Available from: 2012-04-10 Created: 2012-03-22 Last updated: 2018-01-12Bibliographically approved
    2. Towards adaptive zero-knowledge protocols: A case study with Fiat–Shamir identification protocol
    Open this publication in new window or tab >>Towards adaptive zero-knowledge protocols: A case study with Fiat–Shamir identification protocol
    2013 (English)In: Proc. 9th Swedish National Computer Networking Workshop, 2013, p. 67-70Conference paper, Published paper (Refereed)
    Abstract [en]

    Interactive zero-knowledge protocols are used as identification protocols. The protocols are executed in rounds, with security being increased with every round. This allows for a trade-off between security and performance to adapt the protocol to the requirements of the scenario. We experimentally investigate the Fiat–Shamir identification protocol on machines and networks with different performance characteristics. We find that the delay of the protocol highly depends on network latency and upload bandwidth. Computation time becomes more visible, when the protocol transmits little amount of data via a low latency network. We also experience that the impact of the sizes of the variables on the delay of the protocol is less than the number of rounds', which are interior factors in the protocol.

    National Category
    Computer Sciences
    Research subject
    Computer Science with specialization in Computer Communication
    Identifiers
    urn:nbn:se:uu:diva-201070 (URN)
    Conference
    SNCNW 2013
    Projects
    WISENETProFuN
    Available from: 2013-06-05 Created: 2013-06-05 Last updated: 2018-01-11Bibliographically approved
    3. Modelling and analysing a WSN secure aggregation protocol: A comparison of languages and tool support
    Open this publication in new window or tab >>Modelling and analysing a WSN secure aggregation protocol: A comparison of languages and tool support
    2015 (English)Report (Other academic)
    Series
    Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2015-033
    National Category
    Computer Sciences Communication Systems
    Research subject
    Computer Science with specialization in Computer Communication
    Identifiers
    urn:nbn:se:uu:diva-268453 (URN)
    Projects
    ProFuN
    Funder
    Swedish Foundation for Strategic Research , RIT08-0065
    Available from: 2015-12-03 Created: 2015-12-04 Last updated: 2018-01-10Bibliographically approved
  • 25.
    Cambazoglu, Volkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Gutkovas, Ramunas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Åman Pohjola, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Victor, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Modelling and analysing a WSN secure aggregation protocol: A comparison of languages and tool support2015Report (Other academic)
  • 26.
    Carlos, Perez Penichet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Varshney, Ambuj
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Augmenting IoT networks with backscatter-enabled passive sensor tags2016In: Proceedings of the 3rd Workshop on Hot Topics in Wireless, 2016, p. 23-27Conference paper (Refereed)
    Abstract [en]

    The sensing modalities available in an Internet-of-Things (IoT) network are usually fixed before deployment, when the operator selects a suitable IoT platform. Retrofitting a deployment with additional sensors can be cumbersome, because it requires either modifying the deployed hardware or adding new devices that then have to be maintained. In this paper, we present our vision and work towards passive sensor tags: battery-free devices that allow to augment existing IoT deployments with additional sensing capabilities without the need to modify the existing deployment. Our passive sensor tags use backscatter transmissions to communicate with the deployed network. Crucially, they do this in a way that is compatible with the deployed network's radio protocol, and without the need for additional infrastructure. We present an FPGA-based prototype of a passive sensor tag that can communicate with unmodified 802.15.4 IoT devices. Our initial experiments with the prototype support the feasibility of our approach. We also lay out the next steps towards fully realizing the vision of passive sensor tags.

  • 27.
    Carlos, Perez Penichet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Noda, Claro
    Mid-Sweden University, Sweden.
    Varshney, Ambuj
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Battery-free 802.15. 4 Receiver2018In: 7th ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN), IEEE, 2018Conference paper (Refereed)
    Abstract [en]

    We present the architecture of an 802.15.4 receiver that, for the first time, operates at a few hundred microwatts, enabling new battery-free applications. To reach the required micro-power consumption, the architecture diverges from that of commodity receivers in two important ways. First, it offloads the power-hungry local oscillator to an external device, much like backscatter transmitters do. Second, we avoid the energy cost of demodulating a phase-modulated signal by treating 802.15.4 as a frequency-modulated one, which allows us to receive with a simple passive detector and an energy-efficient thresholding circuit. We describe a prototype that can receive 802.15.4 frames with a power consumption of 361 μW. Our receiver prototype achieves sufficient communication range to integrate with deployed wireless sensor networks (WSNs). We illustrate this integration by pairing the prototype with an 802.15.4 backscatter transmitter and integrating it with unmodified 802.15.4 sensor nodes running the TSCH and Glossy protocols.

  • 28.
    Carlos, Perez Penichet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Noda, Claro
    Mid-Sweden University, Sweden.
    Varshney, Ambuj
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Demo Abstract: Battery-Free 802.15.4 Receiver2018In: 17th ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN), IEEE, 2018, p. 130-131Conference paper (Refereed)
    Abstract [en]

    We present the architecture for an 802.15.4 receiver that enables battery-free operation. To reach micro-power consumption, the architecture diverges from that of commodity receivers in the following ways: First, similar to backscatter transmitters, it offloads the power-hungry local oscillator to an external device. Second, we avoid the energy cost of demodulating a phase-modulated signal by treating 802.15.4 as a frequency-modulated one, allowing us to receive with a simple passive detector and an energy-efficient thresholding circuit. We demonstrate an off-the-shelf prototype of our receiver receives 802.15.4 from a distance of 470 cm with the carrier generator 30 cm away. This range is sufficient to integrate with deployed wireless sensor networks (WSNs). We demonstrate this integration by pairing our receiver with a 802.15.4 backscatter transmitter and integrating it with unmodified commodity sensor nodes running the TSCH protocol.

  • 29.
    Carlos, Perez Penichet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. Uppsala Univ, Uppsala, Sweden.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. RISE SICS, Lulea, Sweden.
    Carrier Scheduling in IoT Networks with Interoperable Battery-free Backscatter Tags2019In: IPSN '19: Proceedings of the 2019 International Conference on Information Processing in Sensor Networks, Association for Computing Machinery (ACM), 2019, p. 329-330Conference paper (Refereed)
    Abstract [en]

    New battery-free backscatter tags that integrate with unmodified standard IoT devices can extend the latter's sensing capabilities in a scalable and cost effective way. Existing IoT nodes can provide the unmodulated carrier needed by the new nodes, avoiding the need for additional infrastructure. This, however, puts extra energetic demands on constrained IoT nodes while increasing interference and contention in the network. We use a slotted MAC protocol to guarantee synchronization between transmitters, receivers and carrier generators. We then express the slot allocation problem as a Constraint Optimization Problem (COP) that parallelizes interrogations to battery-free tags when they do not collide with each other and reuses carriers for multiple tags looking to minimize the total time and the number of carrier generators needed to interrogate a set of tags. In networks with sufficient battery-free nodes we obtain a 25% reduction in the number of necessary carriers and a 50% decrease in interrogation time in most cases; leading to significant energy savings, reduced collisions and improved latency.

  • 30.
    Carlos, Pérez Penichet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    On Limits of Constructive Interference in Backscatter Systems2017In: Global Internet of Things Summit (GIoTS), 2017, IEEE, 2017, p. 178-182Conference paper (Other academic)
    Abstract [en]

    Backscatter communication reduces the energy consumption of resource-constrained sensors and actuators by several orders of magnitude as it avoids the resource-consuming need to generate a radio wave. Many backscatter systems and applications suffer from low communication range. By exploiting the collective power of several tags that transmit the same data simultaneously, constructive interference may help to remedy this problem and increase the communication range. When several tags backscatter the same signal simultaneously it is not necessarily true that constructive interference occurs. As our theoretical results and previous work indicate the interference might also be destructive. Our experimental results on real hardware suggest that exploiting constructive interference to increase the communication range requires careful coordination which is difficult in decentralized settings.

  • 31.
    Carlson, Trevor E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Heirman, Wim
    Intel, ExaSci Lab, Santa Clara, CA USA..
    Allam, Osman
    Univ Ghent, B-9000 Ghent, Belgium..
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Eeckhout, Lieven
    Univ Ghent, B-9000 Ghent, Belgium..
    The Load Slice Core Microarchitecture2015In: 2015 ACM/IEEE 42Nd Annual International Symposium On Computer Architecture (ISCA), 2015, p. 272-284Conference paper (Refereed)
    Abstract [en]

    Driven by the motivation to expose instruction-level parallelism (ILP), microprocessor cores have evolved from simple, in-order pipelines into complex, superscalar out-of-order designs. By extracting ILP, these processors also enable parallel cache and memory operations as a useful side-effect. Today, however, the growing off-chip memory wall and complex cache hierarchies of many-core processors make cache and memory accesses ever more costly. This increases the importance of extracting memory hierarchy parallelism (MHP), while reducing the net impact of more general, yet complex and power-hungry ILP-extraction techniques. In addition, for multi-core processors operating in power- and energy-constrained environments, energy-efficiency has largely replaced single-thread performance as the primary concern. Based on this observation, we propose a core microarchitecture that is aimed squarely at generating parallel accesses to the memory hierarchy while maximizing energy efficiency. The Load Slice Core extends the efficient in-order, stall-on-use core with a second in-order pipeline that enables memory accesses and address-generating instructions to bypass stalled instructions in the main pipeline. Backward program slices containing address-generating instructions leading up to loads and stores are extracted automatically by the hardware, using a novel iterative algorithm that requires no software support or recompilation. On average, the Load Slice Core improves performance over a baseline in-order processor by 53% with overheads of only 15% in area and 22% in power, leading to an increase in energy efficiency (MIPS/Watt) over in-order and out-of-order designs by 43% and over 4.7x, respectively. In addition, for a power- and area-constrained many-core design, the Load Slice Core outperforms both in-order and out-of-order designs, achieving a 53% and 95% higher performance, respectively, thus providing an alternative direction for future many-core processors.

  • 32.
    Carlson, Trevor E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Tran, Kim-Anh
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Jimborean, Alexandra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Koukos, Konstantinos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Själander, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Transcending hardware limits with software out-of-order processing2017In: IEEE Computer Architecture Letters, ISSN 1556-6056, Vol. 16, no 2, p. 162-165Article in journal (Refereed)
  • 33.
    Ceballos, Germán
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    How to make tasks faster: Revealing the complex interactions of tasks in the memory system2017In: Proc. Companion 8th ACM International Conference on Systems, Programming, Languages, and Applications: Software for Humanity, New York: ACM Press, 2017, p. 1-3Conference paper (Refereed)
  • 34.
    Ceballos, Germán
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Modeling the interactions between tasks and the memory system2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Making computer systems more energy efficient while obtaining the maximum performance possible is key for future developments in engineering, medicine, entertainment, etc. However it has become a difficult task due to the increasing complexity of hardware and software, and their interactions. For example, developers have to deal with deep, multi-level cache hierarchies on modern CPUs, and keep busy thousands of cores in GPUs, which makes the programming process more difficult.

    To simplify this task, new abstractions and programming models are becoming popular. Their goal is to make applications more scalable and efficient, while still providing the flexibility and portability of old, widely adopted models. One example of this is task-based programming, where simple independent tasks (functions) are delegated to a runtime system which orchestrates their execution. This approach has been successful because the runtime can automatically distribute work across hardware cores and has the potential to minimize data movement and placement (e.g., being aware of the cache hierarchy).

    To build better runtime systems, it is crucial to understand bottlenecks in the performance of current and future multicore systems. In this thesis, we provide fast, accurate and mathematically-sound models and techniques to understand the execution of task-based applications concerning three key aspects: memory behavior (data locality), scheduling, and performance. With these methods, we lay the groundwork for improving runtime system, providing insight into the interplay between the schedule's behavior, data reuse through the cache hierarchy, and the resulting performance.

    List of papers
    1. Shared Resource Sensitivity in Task-Based Runtime Systems
    Open this publication in new window or tab >>Shared Resource Sensitivity in Task-Based Runtime Systems
    2013 (English)In: Proc. 6th Swedish Workshop on Multi-Core Computing, Halmstad University Press, 2013Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Halmstad University Press, 2013
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-212780 (URN)
    Conference
    MCC13, November 25–26, Halmstad, Sweden
    Projects
    Resource Sharing ModelingUPMARC
    Funder
    Swedish Research Council
    Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2018-11-16Bibliographically approved
    2. Formalizing data locality in task parallel applications
    Open this publication in new window or tab >>Formalizing data locality in task parallel applications
    2016 (English)In: Algorithms and Architectures for Parallel Processing, Springer, 2016, p. 43-61Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Springer, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 ; 10049
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-310341 (URN)10.1007/978-3-319-49956-7_4 (DOI)000389797000004 ()978-3-319-49955-0 (ISBN)
    Conference
    ICA3PP 2016, December 14–16, Granada, Spain
    Projects
    UPMARCResource Sharing Modeling
    Funder
    Swedish Foundation for Strategic Research , FFL12-0051
    Available from: 2016-11-19 Created: 2016-12-14 Last updated: 2018-11-16Bibliographically approved
    3. TaskInsight: Understanding task schedules effects on memory and performance
    Open this publication in new window or tab >>TaskInsight: Understanding task schedules effects on memory and performance
    2017 (English)In: Proc. 8th International Workshop on Programming Models and Applications for Multicores and Manycores, New York: ACM Press, 2017, p. 11-20Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    New York: ACM Press, 2017
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-315033 (URN)10.1145/3026937.3026943 (DOI)978-1-4503-4883-6 (ISBN)
    Conference
    PMAM 2017, February 4–8, Austin, TX
    Projects
    UPMARCResource Sharing Modeling
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research , FFL12-0051EU, Horizon 2020, 687698
    Available from: 2017-02-04 Created: 2017-02-08 Last updated: 2018-11-16Bibliographically approved
    4. Analyzing performance variation of task schedulers with TaskInsight
    Open this publication in new window or tab >>Analyzing performance variation of task schedulers with TaskInsight
    2018 (English)In: Parallel Computing, ISSN 0167-8191, E-ISSN 1872-7336, Vol. 75, p. 11-27Article in journal (Refereed) Published
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-340202 (URN)10.1016/j.parco.2018.02.003 (DOI)000433655700002 ()
    Projects
    UPMARCResource Sharing Modeling
    Funder
    Swedish Research Council, FFL12-0051Swedish Foundation for Strategic Research , FFL12-0051
    Available from: 2018-02-22 Created: 2018-01-26 Last updated: 2018-11-16Bibliographically approved
  • 35.
    Ceballos, Germán
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Understanding Task Parallelism: Providing insight into scheduling, memory, and performance for CPUs and Graphics2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Maximizing the performance of computer systems while making them more energy efficient is vital for future developments in engineering, medicine, entertainment, etc. However, the increasing complexity of software, hardware, and their interactions makes this task difficult. Software developers have to deal with complex memory architectures such as multilevel caches on modern CPUs and keeping thousands of cores busy in GPUs, which makes the programming process harder.

    Task-based programming provides high-level abstractions to simplify the development process. In this model, independent tasks (functions) are submitted to a runtime system, which orchestrates their execution across hardware resources. This approach has become popular and successful because the runtime can distribute the workload across hardware resources automatically, and has the potential to optimize the execution to minimize data movement (e.g., being aware of the cache hierarchy).

    However, to build better runtime systems, we now need to understand bottlenecks in the performance of current and future multicore architectures. Unfortunately, since most current work was designed for sequential or thread-based workloads, there is an overall lack of tools and methods to gain insight about the execution of these applications, allowing both the runtime and the programmers to detect potential optimizations.

    In this thesis, we address this lack of tools by providing fast, accurate and mathematically-sound models to understand the execution of task-based applications. In particular, we center these models around three key aspects of the execution: memory behavior (data locality), scheduling, and performance. Our contributions provide insight into the interplay between the schedule's behavior, data reuse through the cache hierarchy, and the resulting performance. These contributions lay the groundwork for improving runtime systems. We first apply these methods to analyze a diverse set of CPU applications, and then leverage them to one of the most common workloads in current systems: graphics rendering on GPUs.

    List of papers
    1. Shared Resource Sensitivity in Task-Based Runtime Systems
    Open this publication in new window or tab >>Shared Resource Sensitivity in Task-Based Runtime Systems
    2013 (English)In: Proc. 6th Swedish Workshop on Multi-Core Computing, Halmstad University Press, 2013Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Halmstad University Press, 2013
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-212780 (URN)
    Conference
    MCC13, November 25–26, Halmstad, Sweden
    Projects
    Resource Sharing ModelingUPMARC
    Funder
    Swedish Research Council
    Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2018-11-16Bibliographically approved
    2. Formalizing data locality in task parallel applications
    Open this publication in new window or tab >>Formalizing data locality in task parallel applications
    2016 (English)In: Algorithms and Architectures for Parallel Processing, Springer, 2016, p. 43-61Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Springer, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 ; 10049
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-310341 (URN)10.1007/978-3-319-49956-7_4 (DOI)000389797000004 ()978-3-319-49955-0 (ISBN)
    Conference
    ICA3PP 2016, December 14–16, Granada, Spain
    Projects
    UPMARCResource Sharing Modeling
    Funder
    Swedish Foundation for Strategic Research , FFL12-0051
    Available from: 2016-11-19 Created: 2016-12-14 Last updated: 2018-11-16Bibliographically approved
    3. Analyzing performance variation of task schedulers with TaskInsight
    Open this publication in new window or tab >>Analyzing performance variation of task schedulers with TaskInsight
    2018 (English)In: Parallel Computing, ISSN 0167-8191, E-ISSN 1872-7336, Vol. 75, p. 11-27Article in journal (Refereed) Published
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-340202 (URN)10.1016/j.parco.2018.02.003 (DOI)000433655700002 ()
    Projects
    UPMARCResource Sharing Modeling
    Funder
    Swedish Research Council, FFL12-0051Swedish Foundation for Strategic Research , FFL12-0051
    Available from: 2018-02-22 Created: 2018-01-26 Last updated: 2018-11-16Bibliographically approved
    4. Behind the Scenes: Memory Analysis of Graphical Workloads on Tile-based GPUs
    Open this publication in new window or tab >>Behind the Scenes: Memory Analysis of Graphical Workloads on Tile-based GPUs
    2018 (English)In: Proc. International Symposium on Performance Analysis of Systems and Software: ISPASS 2018, IEEE Computer Society, 2018, p. 1-11Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    IEEE Computer Society, 2018
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-361214 (URN)10.1109/ISPASS.2018.00009 (DOI)978-1-5386-5010-3 (ISBN)
    Conference
    ISPASS 2018, April 2–4, Belfast, UK
    Projects
    UPMARC
    Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2018-11-16Bibliographically approved
    5. Tail-PASS: Resource-based Cache Management for Tiled Graphics Rendering Hardware
    Open this publication in new window or tab >>Tail-PASS: Resource-based Cache Management for Tiled Graphics Rendering Hardware
    2018 (English)In: Proc. 16th International Conference on Parallel and Distributed Processing with Applications, IEEE, 2018, p. 55-63Conference paper, Published paper (Refereed)
    Abstract [en]

    Modern graphics rendering is a very expensive process and can account for 60% of the battery consumption on current games. Much of the cost comes from the high memory bandwidth of rendering complex graphics. To render a frame, multiple smaller rendering passes called scenes are executed, with each one tiled for parallel execution. The data for each scene comes from hundreds of software resources (textures). We observe that each frame can consume up to 1000s of MB of data, but that over 75% of the graphics memory accesses are to the top-10 resources, and that bypassing the remaining infrequently accessed (tail) resources reduces cache pollution. Bypassing the tail can save up to 35% of the main memory traffic over resource-oblivious replacement policies and cache management techniques. In this paper, we propose Tail-PASS, a cache management technique that detects the most accessed resources at runtime, learns if it is worth bypassing the least accessed ones, and then dynamically enables/disables bypassing to reduce cache pollution on a per-scene basis. Overall, we see an average reduction in bandwidth-per-frame of 22% (up to 46%) by bypassing all but the top-10 resources and an 11% (up to 44%) reduction if only the top-2 resources are cached.

    Place, publisher, year, edition, pages
    IEEE, 2018
    National Category
    Computer Systems Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-363920 (URN)10.1109/BDCloud.2018.00022 (DOI)000467843200008 ()978-1-7281-1141-4 (ISBN)
    Conference
    ISPA 2018, December 11–13, Melbourne, Australia
    Funder
    EU, European Research Council, 715283
    Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2019-06-17Bibliographically approved
  • 36.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Spatial and Temporal Cache Sharing Analysis in Tasks2016Conference paper (Other academic)
  • 37.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Grass, Thomas
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hugo, Andra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Characterizing Task Scheduling Performance Based on Data Reuse2016In: Proc. 9th Nordic Workshop on Multi-Core Computing, 2016Conference paper (Refereed)
  • 38.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Grass, Thomas
    Hugo, Andra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Analyzing performance variation of task schedulers with TaskInsight2018In: Parallel Computing, ISSN 0167-8191, E-ISSN 1872-7336, Vol. 75, p. 11-27Article in journal (Refereed)
  • 39.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Grass, Thomas
    Hugo, Andra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    TaskInsight: Understanding task schedules effects on memory and performance2017In: Proc. 8th International Workshop on Programming Models and Applications for Multicores and Manycores, New York: ACM Press, 2017, p. 11-20Conference paper (Refereed)
  • 40.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Formalizing data locality in task parallel applications2016In: Algorithms and Architectures for Parallel Processing, Springer, 2016, p. 43-61Conference paper (Refereed)
  • 41.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    StatTask: Reuse distance analysis for task-based applications2015In: Proc. 7th Workshop on Rapid Simulation and Performance Evaluation: Methods and Tools, New York: ACM Press, 2015, p. 1-7Conference paper (Refereed)
  • 42.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Tail-PASS: Resource-based Cache Management for Tiled Graphics Rendering Hardware2018In: Proc. 16th International Conference on Parallel and Distributed Processing with Applications, IEEE, 2018, p. 55-63Conference paper (Refereed)
    Abstract [en]

    Modern graphics rendering is a very expensive process and can account for 60% of the battery consumption on current games. Much of the cost comes from the high memory bandwidth of rendering complex graphics. To render a frame, multiple smaller rendering passes called scenes are executed, with each one tiled for parallel execution. The data for each scene comes from hundreds of software resources (textures). We observe that each frame can consume up to 1000s of MB of data, but that over 75% of the graphics memory accesses are to the top-10 resources, and that bypassing the remaining infrequently accessed (tail) resources reduces cache pollution. Bypassing the tail can save up to 35% of the main memory traffic over resource-oblivious replacement policies and cache management techniques. In this paper, we propose Tail-PASS, a cache management technique that detects the most accessed resources at runtime, learns if it is worth bypassing the least accessed ones, and then dynamically enables/disables bypassing to reduce cache pollution on a per-scene basis. Overall, we see an average reduction in bandwidth-per-frame of 22% (up to 46%) by bypassing all but the top-10 resources and an 11% (up to 44%) reduction if only the top-2 resources are cached.

  • 43.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Understanding the interplay between task scheduling, memory and performance2017In: Proc. Companion 8th ACM International Conference on Systems, Programming, Languages, and Applications: Software for Humanity, New York: ACM Press, 2017, p. 21-23Conference paper (Refereed)
  • 44.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hugo, Andra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Exploring scheduling effects on task performance with TaskInsight2017In: Supercomputing frontiers and innovations, ISSN 2214-3270, E-ISSN 2313-8734, Vol. 4, no 3, p. 91-98Article in journal (Refereed)
  • 45.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Sembrant, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Carlson, Trevor E.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Analyzing Graphics Workloads on Tile-based GPUs2017In: Proc. 20th International Symposium on Workload Characterization, IEEE, 2017, p. 108-109Conference paper (Refereed)
  • 46.
    Ceballos, Germán
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Sembrant, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Carlson, Trevor E.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Behind the Scenes: Memory Analysis of Graphical Workloads on Tile-based GPUs2018In: Proc. International Symposium on Performance Analysis of Systems and Software: ISPASS 2018, IEEE Computer Society, 2018, p. 1-11Conference paper (Refereed)
  • 47. Cebrián, Juan M.
    et al.
    Fernández-Pascual, Ricardo
    Jimborean, Alexandra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Acacio, Manuel E.
    Ros, Alberto
    A dedicated private-shared cache design for scalable multiprocessors2017In: Concurrency and Computation, ISSN 1532-0626, E-ISSN 1532-0634, Vol. 29, no 2, article id e3871Article in journal (Refereed)
  • 48.
    Cojean, Terry
    et al.
    University of Bordeaux.
    Guermouche, Abdou
    University of Bordeaux.
    Hugo, Andra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Namyst, Raymond
    University of Bordeaux.
    Wacrenier, Pierre-André
    University of Bordeaux.
    Resource aggregation for task-based CholeskyFactorization on top of heterogeneous machines2016Conference paper (Refereed)
  • 49.
    Davari, Mahdad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Advances Towards Data-Race-Free Cache Coherence Through Data Classification2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Providing a consistent view of the shared memory based on precise and well-defined semantics—memory consistency model—has been an enabling factor in the widespread acceptance and commercial success of shared-memory architectures. Moreover, cache coherence protocols have been employed by the hardware to remove from the programmers the burden of dealing with the memory inconsistency that emerges in the presence of the private caches. The principle behind all such cache coherence protocols is to guarantee that consistent values are read from the private caches at all times.

    In its most stringent form, a cache coherence protocol eagerly enforces two invariants before each data modification: i) no other core has a copy of the data in its private caches, and ii) all other cores know where to receive the consistent data should they need the data later. Nevertheless, by partly transferring the responsibility for maintaining those invariants to the programmers, commercial multicores have adopted weaker memory consistency models, namely the Total Store Order (TSO), in order to optimize the performance for more common cases.

    Moreover, memory models with more relaxed invariants have been proposed based on the observation that more and more software is written in compliance with the Data-Race-Free (DRF) semantics. The semantics of DRF software can be leveraged by the hardware to infer when data in the private caches might be inconsistent. As a result, hardware ignores the inconsistent data and retrieves the consistent data from the shared memory. DRF semantics therefore removes from the hardware the burden of eagerly enforcing the strong consistency invariants before each data modification. Instead, consistency is guaranteed only when needed. This results in manifold optimizations, such as reducing the energy consumption and improving the performance and scalability. The efficiency of detecting and discarding the inconsistent data is an important factor affecting the efficiency of such coherence protocols. For instance, discarding the consistent data does not affect the correctness, but results in performance loss and increased energy consumption.

    In this thesis we show how data classification can be leveraged as an effective tool to simplify the cache coherence based on the DRF semantics. In particular, we introduce simple but efficient hardware-based private/shared data classification techniques that can be used to efficiently detect the inconsistent data, thus enabling low-overhead and scalable cache coherence solutions based on the DRF semantics.

    List of papers
    1. Hierarchical private/shared classification: The key to simple and efficient coherence for clustered cache hierarchies
    Open this publication in new window or tab >>Hierarchical private/shared classification: The key to simple and efficient coherence for clustered cache hierarchies
    2015 (English)In: Proc. 21st International Symposium on High Performance Computer Architecture, IEEE Computer Society Digital Library, 2015, p. 186-197Conference paper, Published paper (Refereed)
    Abstract [en]

    Hierarchical clustered cache designs are becoming an appealing alternative for multicores. Grouping cores and their caches in clusters reduces network congestion by localizing traffic among several hierarchical levels, potentially enabling much higher scalability. While such architectures can be formed recursively by replicating a base design pattern, keeping the whole hierarchy coherent requires more effort and consideration. The reason is that, in hierarchical coherence, even basic operations must be recursive. As a consequence, intermediate-level caches behave both as directories and as leaf caches. This leads to an explosion of states, protocol-races, and protocol complexity. While there have been previous efforts to extend directory-based coherence to hierarchical designs their increased complexity and verification cost is a serious impediment to their adoption. We aim to address these concerns by encapsulating all hierarchical complexity in a simple function: that of determining when a data block is shared entirely within a cluster (sub-tree of the hierarchy) and is private from the outside. This allows us to eliminate complex recursive operations that span the hierarchy and instead employ simple coherence mechanisms such as self-invalidation and write-through-now restricted to operate within the cluster where a data block is shared. We examine two inclusivity options and discuss the relation of our approach to the recently proposed Hierarchical-Race-Free (HRF) memory models. Finally, comparisons to a hierarchical directory-based MOESI, VIPS-M, and TokenCMP protocols show that, despite its simplicity our approach results in competitive performance and decreased network traffic.

    Place, publisher, year, edition, pages
    IEEE Computer Society Digital Library, 2015
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-265651 (URN)10.1109/HPCA.2015.7056032 (DOI)000380564900016 ()9781479989300 (ISBN)
    External cooperation:
    Conference
    HPCA 2015, February 7–11, Burlingame, CA
    Available from: 2015-02-11 Created: 2015-11-02 Last updated: 2017-04-22Bibliographically approved
    2. The effects of granularity and adaptivity on private/shared classification for coherence
    Open this publication in new window or tab >>The effects of granularity and adaptivity on private/shared classification for coherence
    2015 (English)In: ACM Transactions on Architecture and Code Optimization (TACO), ISSN 1544-3566, E-ISSN 1544-3973, Vol. 12, no 3, article id 26Article in journal (Refereed) Published
    Abstract [en]

    Classification of data into private and shared has proven to be a catalyst for techniques to reduce coherence cost, since private data can be taken out of coherence and resources can be concentrated on providing coherence for shared data. In this article, we examine how granularity-page-level versus cache-line level- and adaptivity-going from shared to private-affect the outcome of classification and its final impact on coherence. We create a classification technique, called Generational Classification, and a coherence protocol called Generational Coherence, which treats data as private or shared based on cache-line generations. We compare two coherence protocols based on self-invalidation/self-downgrade with respect to data classification. Our findings are enlightening: (i) Some programs benefit from finer granularity, some benefit further from adaptivity, but some do not benefit from either. (ii) Reducing the amount of shared data has no perceptible impact on coherence misses caused by self-invalidation of shared data, hence no impact on performance. (iii) In contrast, classifying more data as private has implications for protocols that employ write-through as a means of self-downgrade, resulting in network traffic reduction-up to 30%-by reducing write-through traffic.

    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-265580 (URN)10.1145/2790301 (DOI)000363004100001 ()
    Available from: 2015-10-06 Created: 2015-11-02 Last updated: 2017-12-01Bibliographically approved
    3. An efficient, self-contained, on-chip directory: DIR1-SISD
    Open this publication in new window or tab >>An efficient, self-contained, on-chip directory: DIR1-SISD
    2015 (English)In: Proc. 24th International Conference on Parallel Architectures and Compilation Techniques, IEEE Computer Society, 2015, p. 317-330Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    IEEE Computer Society, 2015
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-265611 (URN)10.1109/PACT.2015.23 (DOI)000378942700027 ()978-1-4673-9524-3 (ISBN)
    Conference
    PACT 2015, October 18–21, San Francisco, CA
    Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2017-04-22Bibliographically approved
    4. Scope-Aware Classification: Taking the hierarchical private/shared data classification to the next level
    Open this publication in new window or tab >>Scope-Aware Classification: Taking the hierarchical private/shared data classification to the next level
    2017 (English)Report (Other academic)
    Series
    Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2017-008
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-320324 (URN)
    Available from: 2017-04-27 Created: 2017-04-19 Last updated: 2017-07-03Bibliographically approved
    5. The best of both works: A hybrid data-race-free cache coherence scheme
    Open this publication in new window or tab >>The best of both works: A hybrid data-race-free cache coherence scheme
    2017 (English)Report (Other academic)
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-320320 (URN)
    Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-11-15
  • 50.
    Davari, Mahdad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Scope-Aware Classification: Taking the hierarchical private/shared data classification to the next level2017Report (Other academic)
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