Despite the proliferation of multi-core and multi-threaded architectures, exploiting implicit parallelism for a single semantic thread is still a crucial component in achieving high performance. Lookahead is a "tried-and-true" strategy in uncovering implicit parallelism. However, a conventional, monolithic out-of-order core quickly becomes resource-inefficient when looking beyond a small distance. One general approach to mitigate the impact of branch mispredictions and cache misses is to enable deep look-ahead. A particular approach that is both flexible and effective is to use an independent, decoupled look-ahead thread on a separate thread context guided by a program slice known as skeleton. While capable of generating significant performance gains, the look-ahead agent often becomes the new speed limit. We propose to accelerate the look-ahead thread by skipping branch based, side-effect free code modules that do not contribute to the effectiveness of look-ahead. We call them Do-It-Yourself or DIY branches for which the main thread does not get any help from the look-ahead thread, instead relies on its own branch predictor and prefetcher. By skipping DIY branches, look-ahead thread propels ahead and provides performance-critical assistance down the stream to improve the performance of decoupled look-ahead system by up to 15%.
{"title":"Load Balancing in Decoupled Look-ahead: A Do-It-Yourself (DIY) Approach","authors":"Raj Parihar, Michael C. Huang","doi":"10.1109/PACT.2015.55","DOIUrl":"https://doi.org/10.1109/PACT.2015.55","url":null,"abstract":"Despite the proliferation of multi-core and multi-threaded architectures, exploiting implicit parallelism for a single semantic thread is still a crucial component in achieving high performance. Lookahead is a \"tried-and-true\" strategy in uncovering implicit parallelism. However, a conventional, monolithic out-of-order core quickly becomes resource-inefficient when looking beyond a small distance. One general approach to mitigate the impact of branch mispredictions and cache misses is to enable deep look-ahead. A particular approach that is both flexible and effective is to use an independent, decoupled look-ahead thread on a separate thread context guided by a program slice known as skeleton. While capable of generating significant performance gains, the look-ahead agent often becomes the new speed limit. We propose to accelerate the look-ahead thread by skipping branch based, side-effect free code modules that do not contribute to the effectiveness of look-ahead. We call them Do-It-Yourself or DIY branches for which the main thread does not get any help from the look-ahead thread, instead relies on its own branch predictor and prefetcher. By skipping DIY branches, look-ahead thread propels ahead and provides performance-critical assistance down the stream to improve the performance of decoupled look-ahead system by up to 15%.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116969055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A traditional least-recently used (LRU) cache replacement policy fails to achieve the performance of the optimal replacement policy when cache blocks with diverse reuse characteristics interfere with each other. When multiple applications share a cache, it is often partitioned among the applications because cache blocks show similar reuse characteristics within each application. In this paper, we extend the idea to a single application by viewing a cache as a shared resource between individual memory instructions. To that end, we propose Instruction-based LRU (ILRU), a fine grain cache partitioning that way-partitions individual cache sets based on per-instruction working blocks, which are cache blocks required by an instruction to satisfy all the reuses within a set. In ILRU, a memory instruction steals a block from another only when it requires more blocks than it currently has. Otherwise, a memory instruction victimizes among the cache blocks inserted by itself. Experiments show that ILRU can improve the cache performance in all levels of cache, reducing the number of misses by an average of 7.0% for L1, 9.1% for L2, and 8.7% for L3, which results in a geometric mean performance improvement of 5.3%. ILRU for a three-level cache hierarchy imposes a modest 1.3% storage overhead over the total cache size.
{"title":"Fine Grain Cache Partitioning Using Per-Instruction Working Blocks","authors":"Jason Jong Kyu Park, Yongjun Park, S. Mahlke","doi":"10.1109/PACT.2015.11","DOIUrl":"https://doi.org/10.1109/PACT.2015.11","url":null,"abstract":"A traditional least-recently used (LRU) cache replacement policy fails to achieve the performance of the optimal replacement policy when cache blocks with diverse reuse characteristics interfere with each other. When multiple applications share a cache, it is often partitioned among the applications because cache blocks show similar reuse characteristics within each application. In this paper, we extend the idea to a single application by viewing a cache as a shared resource between individual memory instructions. To that end, we propose Instruction-based LRU (ILRU), a fine grain cache partitioning that way-partitions individual cache sets based on per-instruction working blocks, which are cache blocks required by an instruction to satisfy all the reuses within a set. In ILRU, a memory instruction steals a block from another only when it requires more blocks than it currently has. Otherwise, a memory instruction victimizes among the cache blocks inserted by itself. Experiments show that ILRU can improve the cache performance in all levels of cache, reducing the number of misses by an average of 7.0% for L1, 9.1% for L2, and 8.7% for L3, which results in a geometric mean performance improvement of 5.3%. ILRU for a three-level cache hierarchy imposes a modest 1.3% storage overhead over the total cache size.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127126184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Summary form only given. I will describe a decade-long, multi-disciplinary, multi-institutional effort spanning neuroscience, supercomputing, and nanotechnology to build and demonstrate a brain-inspired computer and describe the architecture, programming model, and applications. I will also describe future efforts to build, literally, "brain-in-a-box". For more information, see: modha.org.
{"title":"Brain-Inspired Computing","authors":"D. Modha","doi":"10.1109/PACT.2015.49","DOIUrl":"https://doi.org/10.1109/PACT.2015.49","url":null,"abstract":"Summary form only given. I will describe a decade-long, multi-disciplinary, multi-institutional effort spanning neuroscience, supercomputing, and nanotechnology to build and demonstrate a brain-inspired computer and describe the architecture, programming model, and applications. I will also describe future efforts to build, literally, \"brain-in-a-box\". For more information, see: modha.org.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123268777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jie Zhang, D. Donofrio, J. Shalf, M. Kandemir, Myoungsoo Jung
Thanks to massive parallelism in modern Graphics Processing Units (GPUs), emerging data processing applications in GPU computing exhibit ten-fold speedups compared to CPU-only systems. However, this GPU-based acceleration is limited in many cases by the significant data movement overheads and inefficient memory management for host-side storage accesses. To address these shortcomings, this paper proposes a non-volatile memory management unit (NVMMU) that reduces the file data movement overheads by directly connecting the Solid State Disk (SSD) to the GPU. We implemented our proposed NVMMU on a real hardware with commercially available GPU and SSD devices by considering different types of storage interfaces and configurations. In this work, NVMMU unifies two discrete software stacks (one for the SSD and other for the GPU) in two major ways. While a new interface provided by our NVMMU directly forwards file data between the GPU runtime library and the I/O runtime library, it supports non-volatile direct memory access (NDMA) that pairs those GPU and SSD devices via physically shared system memory blocks. This unification in turn can eliminate unnecessary user/kernel-mode switching, improve memory management, and remove data copy overheads. Our evaluation results demonstrate that NVMMU can reduce the overheads of file data movement by 95% on average, improving overall system performance by 78% compared to a conventional IOMMU approach.
{"title":"NVMMU: A Non-volatile Memory Management Unit for Heterogeneous GPU-SSD Architectures","authors":"Jie Zhang, D. Donofrio, J. Shalf, M. Kandemir, Myoungsoo Jung","doi":"10.1109/PACT.2015.43","DOIUrl":"https://doi.org/10.1109/PACT.2015.43","url":null,"abstract":"Thanks to massive parallelism in modern Graphics Processing Units (GPUs), emerging data processing applications in GPU computing exhibit ten-fold speedups compared to CPU-only systems. However, this GPU-based acceleration is limited in many cases by the significant data movement overheads and inefficient memory management for host-side storage accesses. To address these shortcomings, this paper proposes a non-volatile memory management unit (NVMMU) that reduces the file data movement overheads by directly connecting the Solid State Disk (SSD) to the GPU. We implemented our proposed NVMMU on a real hardware with commercially available GPU and SSD devices by considering different types of storage interfaces and configurations. In this work, NVMMU unifies two discrete software stacks (one for the SSD and other for the GPU) in two major ways. While a new interface provided by our NVMMU directly forwards file data between the GPU runtime library and the I/O runtime library, it supports non-volatile direct memory access (NDMA) that pairs those GPU and SSD devices via physically shared system memory blocks. This unification in turn can eliminate unnecessary user/kernel-mode switching, improve memory management, and remove data copy overheads. Our evaluation results demonstrate that NVMMU can reduce the overheads of file data movement by 95% on average, improving overall system performance by 78% compared to a conventional IOMMU approach.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115177863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Adam McLaughlin, D. Merrill, M. Garland, David A. Bader
Contemporary microprocessors use relaxed memory consistency models to allow for aggressive optimizations in hardware. This enhancement in performance comes at the cost of design complexity and verification effort. In particular, verifying an execution of a program against its system's memory consistency model is an NP-complete problem. Several graph-based approximations to this problem based on carefully constructed randomized test programs have been proposed in the literature, however, such approaches are sequential and execute slowly on large graphs of interest. Unfortunately, the ability to execute larger tests is tremendously important, since such tests enable one to expose bugs more quickly. Successfully executing more tests per unit time is also desirable, since it allows for one to check for a greater variety of errors in the memory subsystem by utilizing a more diverse set of tests. This paper improves upon existing work by introducing an algorithm that not only reduces the time complexity of the verification process, but also facilitates the development of parallel algorithms for solving these problems. We first show performance improvements from a sequential approach and gain further performance from parallel implementations in OpenMP and CUDA. For large tests of interest, our GPU implementation achieves an average application speedup of 26.36x over existing techniques in use at NVIDIA.
{"title":"Parallel Methods for Verifying the Consistency of Weakly-Ordered Architectures","authors":"Adam McLaughlin, D. Merrill, M. Garland, David A. Bader","doi":"10.1109/PACT.2015.18","DOIUrl":"https://doi.org/10.1109/PACT.2015.18","url":null,"abstract":"Contemporary microprocessors use relaxed memory consistency models to allow for aggressive optimizations in hardware. This enhancement in performance comes at the cost of design complexity and verification effort. In particular, verifying an execution of a program against its system's memory consistency model is an NP-complete problem. Several graph-based approximations to this problem based on carefully constructed randomized test programs have been proposed in the literature, however, such approaches are sequential and execute slowly on large graphs of interest. Unfortunately, the ability to execute larger tests is tremendously important, since such tests enable one to expose bugs more quickly. Successfully executing more tests per unit time is also desirable, since it allows for one to check for a greater variety of errors in the memory subsystem by utilizing a more diverse set of tests. This paper improves upon existing work by introducing an algorithm that not only reduces the time complexity of the verification process, but also facilitates the development of parallel algorithms for solving these problems. We first show performance improvements from a sequential approach and gain further performance from parallel implementations in OpenMP and CUDA. For large tests of interest, our GPU implementation achieves an average application speedup of 26.36x over existing techniques in use at NVIDIA.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128281290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Advances in die-stacking (3D) technology have enabled the tight integration of significant quantities of DRAM with high-performance computation logic. How to integrate this technology into the overall architecture of a computing system is an open question. While much recent effort has focused on hardware-based techniques for using die-stacked memory (e.g., caching), in this paper we explore what it takes for a software-driven approach to be effective. First we consider exposing die-stacked DRAM directly to applications, relying on the static partitioning of allocations between fast on-chip and slow off-chip DRAM. We see only marginal benefits from this approach (9% speedup). Next, we explore OS-based page caches that dynamically partition application memory, but we find such approaches to be worse than not having stacked DRAM at all! We analyze the performance bottlenecks in OS page caches, and propose two simple techniques that make the OS approach viable. The first is a hardware-assisted TLB shoot-down, which is a more general mechanism that is valuable beyond stacked DRAM, and enables OS-managed page caches to achieve a 27% speedup, the second is a software-implemented prefetcher that extends classic hardware prefetching algorithms to the page level, leading to 39% speedup. With these simple and lightweight components, the OS page cache can provide 70% of the performance benefit that would be achievable with an ideal and unrealistic system where all of main memory is die-stacked. However, we also found that applications with poor locality (e.g., graph analyses) are not amenable to any page-caching schemes -- whether hardware or software -- and therefore we recommend that the system still provides APIs to the application layers to explicitly control die-stacked DRAM allocations.
{"title":"A Software-Managed Approach to Die-Stacked DRAM","authors":"M. Oskin, G. Loh","doi":"10.1109/PACT.2015.30","DOIUrl":"https://doi.org/10.1109/PACT.2015.30","url":null,"abstract":"Advances in die-stacking (3D) technology have enabled the tight integration of significant quantities of DRAM with high-performance computation logic. How to integrate this technology into the overall architecture of a computing system is an open question. While much recent effort has focused on hardware-based techniques for using die-stacked memory (e.g., caching), in this paper we explore what it takes for a software-driven approach to be effective. First we consider exposing die-stacked DRAM directly to applications, relying on the static partitioning of allocations between fast on-chip and slow off-chip DRAM. We see only marginal benefits from this approach (9% speedup). Next, we explore OS-based page caches that dynamically partition application memory, but we find such approaches to be worse than not having stacked DRAM at all! We analyze the performance bottlenecks in OS page caches, and propose two simple techniques that make the OS approach viable. The first is a hardware-assisted TLB shoot-down, which is a more general mechanism that is valuable beyond stacked DRAM, and enables OS-managed page caches to achieve a 27% speedup, the second is a software-implemented prefetcher that extends classic hardware prefetching algorithms to the page level, leading to 39% speedup. With these simple and lightweight components, the OS page cache can provide 70% of the performance benefit that would be achievable with an ideal and unrealistic system where all of main memory is die-stacked. However, we also found that applications with poor locality (e.g., graph analyses) are not amenable to any page-caching schemes -- whether hardware or software -- and therefore we recommend that the system still provides APIs to the application layers to explicitly control die-stacked DRAM allocations.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124018904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The memory subsystem (memory controller, bus, andDRAM) is becoming a bottleneck in computer system performance. Optimizing the design of the multicore memory subsystem requires good understanding of the representative workload. A common practice in designing the memory subsystem is to rely on trace simulation. However, the conventional method of relying on traditional traces faces two major challenges. First, many software users are apprehensive about sharing their code (source or binaries) due to the proprietary nature of the code or secrecy of data, so representative traces are sometimes not available. Second, there is a feedback loop where memory performance affects processor performance, which in turnalters the timing of memory requests that reach the bus. Such feedback loop is difficult to capture with traces. In this paper, we present MeToo, a framework for generating synthetic memory traffic for memory subsystem design exploration. MeToo uses a small set of statistics that summarizes the performance behavior of the original applications, and generates synthetic traces or executables stochastically, allowing applications to remain proprietary. MeToo uses novel methods for mimicking the memory feedback loop. We validate MeToo clones, and show very good fit with the original applications' behavior, with an average error of only 4.2%, which is a small fraction of the errors obtained using geometric inter-arrival(commonly used in queueing models) and uniform inter-arrival.
{"title":"MeToo: Stochastic Modeling of Memory Traffic Timing Behavior","authors":"Yipeng Wang, Ganesh Balakrishnan, Yan Solihin","doi":"10.1109/PACT.2015.36","DOIUrl":"https://doi.org/10.1109/PACT.2015.36","url":null,"abstract":"The memory subsystem (memory controller, bus, andDRAM) is becoming a bottleneck in computer system performance. Optimizing the design of the multicore memory subsystem requires good understanding of the representative workload. A common practice in designing the memory subsystem is to rely on trace simulation. However, the conventional method of relying on traditional traces faces two major challenges. First, many software users are apprehensive about sharing their code (source or binaries) due to the proprietary nature of the code or secrecy of data, so representative traces are sometimes not available. Second, there is a feedback loop where memory performance affects processor performance, which in turnalters the timing of memory requests that reach the bus. Such feedback loop is difficult to capture with traces. In this paper, we present MeToo, a framework for generating synthetic memory traffic for memory subsystem design exploration. MeToo uses a small set of statistics that summarizes the performance behavior of the original applications, and generates synthetic traces or executables stochastically, allowing applications to remain proprietary. MeToo uses novel methods for mimicking the memory feedback loop. We validate MeToo clones, and show very good fit with the original applications' behavior, with an average error of only 4.2%, which is a small fraction of the errors obtained using geometric inter-arrival(commonly used in queueing models) and uniform inter-arrival.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134513153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mahdad Davari, Alberto Ros, Erik Hagersten, S. Kaxiras
Directory-based cache coherence is the de-facto standard for scalable shared-memory multi/many-cores and significant effort is invested in reducing its overhead. However, directory area and complexity optimizations are often antithetical to each other. Novel directory-less coherence schemes have been introduced to remove the complexity and cost associated with directories in their entirety. However, such schemes introduce new challenges by transferring some of the directory complexity and functionality to the OS and using the page table and the TLBs to store data classification information. In this work we bridge the gap between directory-based and directory-less coherence schemes and propose a hybrid scheme called DIR1-SISD which employs self-invalidation and self-downgrade as directory policies for the shared entries. DIR1-SISD allows simultaneous optimizations in area and complexity without relying on the OS. DIR1-SISD keeps track of a single -- private -- owner, or allows multiple-readers-multiple-writers to exist simultaneously by transferring the responsibility for their coherence to the corresponding cores. A DIR1-SISD self-contained directory cache has a unique ability to minimize eviction-induced complexities by allowing directory entries to be evicted without maintaining inclusion with the cached data (thus avoiding the complexities of broadcasts) and without the need to have a backing store. Using simulation we show that a small, self-contained, DIR1-SISD cache outperforms a traditional DIR16-NB MESI protocol with a directory cache embedded in the LLC (8% in execution time and 15% in traffic) and, further, outperforms a SISD protocol that relies on the OS to provide a persistent page-based directory (4% in execution time and 20% in traffic).
{"title":"An Efficient, Self-Contained, On-chip Directory: DIR1-SISD","authors":"Mahdad Davari, Alberto Ros, Erik Hagersten, S. Kaxiras","doi":"10.1109/PACT.2015.23","DOIUrl":"https://doi.org/10.1109/PACT.2015.23","url":null,"abstract":"Directory-based cache coherence is the de-facto standard for scalable shared-memory multi/many-cores and significant effort is invested in reducing its overhead. However, directory area and complexity optimizations are often antithetical to each other. Novel directory-less coherence schemes have been introduced to remove the complexity and cost associated with directories in their entirety. However, such schemes introduce new challenges by transferring some of the directory complexity and functionality to the OS and using the page table and the TLBs to store data classification information. In this work we bridge the gap between directory-based and directory-less coherence schemes and propose a hybrid scheme called DIR1-SISD which employs self-invalidation and self-downgrade as directory policies for the shared entries. DIR1-SISD allows simultaneous optimizations in area and complexity without relying on the OS. DIR1-SISD keeps track of a single -- private -- owner, or allows multiple-readers-multiple-writers to exist simultaneously by transferring the responsibility for their coherence to the corresponding cores. A DIR1-SISD self-contained directory cache has a unique ability to minimize eviction-induced complexities by allowing directory entries to be evicted without maintaining inclusion with the cached data (thus avoiding the complexities of broadcasts) and without the need to have a backing store. Using simulation we show that a small, self-contained, DIR1-SISD cache outperforms a traditional DIR16-NB MESI protocol with a directory cache embedded in the LLC (8% in execution time and 15% in traffic) and, further, outperforms a SISD protocol that relies on the OS to provide a persistent page-based directory (4% in execution time and 20% in traffic).","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131731885","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A new memory coherence protocol, Tardis, is proposed. Tardis uses timestamp counters representing logical time as well as physical time to order memory operations and enforce sequential consistency in any type of shared memory system. Tardis is unique in that as compared to the widely-adopted directory coherence protocol, and its variants, it completely avoids multicasting and only requires O(log N) storage per cache block for an N-core system rather than O(N) sharer information. Tardis is simpler and easier to reason about, yet achieves similar performance to directory protocols on a wide range of benchmarks run on 16, 64 and 256 cores.
{"title":"Tardis: Time Traveling Coherence Algorithm for Distributed Shared Memory","authors":"Xiangyao Yu, S. Devadas","doi":"10.1109/PACT.2015.12","DOIUrl":"https://doi.org/10.1109/PACT.2015.12","url":null,"abstract":"A new memory coherence protocol, Tardis, is proposed. Tardis uses timestamp counters representing logical time as well as physical time to order memory operations and enforce sequential consistency in any type of shared memory system. Tardis is unique in that as compared to the widely-adopted directory coherence protocol, and its variants, it completely avoids multicasting and only requires O(log N) storage per cache block for an N-core system rather than O(N) sharer information. Tardis is simpler and easier to reason about, yet achieves similar performance to directory protocols on a wide range of benchmarks run on 16, 64 and 256 cores.","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131230902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Donghyuk Lee, Lavanya Subramanian, Rachata Ausavarungnirun, Jongmoo Choi, O. Mutlu
Memory channel contention is a critical performance bottleneck in modern systems that have highly parallelized processing units operating on large data sets. The memory channel is contended not only by requests from different user applications (CPU access) but also by system requests for peripheral data (IO access), usually controlled by Direct Memory Access (DMA) engines. Our goal, in this work, is to improve system performance byeliminating memory channel contention between CPU accesses and IO accesses. To this end, we propose a hardware-software cooperative data transfer mechanism, Decoupled DMA (DDMA) that provides a specialized low-cost memory channel for IO accesses. In our DDMA design, main memoryhas two independent data channels, of which one is connected to the processor (CPU channel) and the other to the IO devices (IO channel), enabling CPU and IO accesses to be served on different channels. Systemsoftware or the compiler identifies which requests should be handled on the IO channel and communicates this to the DDMA engine, which then initiates the transfers on the IO channel. By doing so, our proposal increasesthe effective memory channel bandwidth, thereby either accelerating data transfers between system components, or providing opportunities to employ IO performance enhancement techniques (e.g., aggressive IO prefetching)without interfering with CPU accessesWe demonstrate the effectiveness of our DDMA framework in two scenarios: (i) CPU-GPU communication and (ii) in-memory communication (bulk datacopy/initialization within the main memory). By effectively decoupling accesses for CPU-GPU communication and in-memory communication from CPU accesses, our DDMA-based design achieves significant performanceimprovement across a wide variety of system configurations (e.g., 20% average performance improvement on a typical 2-channel 2-rank memory system).
{"title":"Decoupled Direct Memory Access: Isolating CPU and IO Traffic by Leveraging a Dual-Data-Port DRAM","authors":"Donghyuk Lee, Lavanya Subramanian, Rachata Ausavarungnirun, Jongmoo Choi, O. Mutlu","doi":"10.1109/PACT.2015.51","DOIUrl":"https://doi.org/10.1109/PACT.2015.51","url":null,"abstract":"Memory channel contention is a critical performance bottleneck in modern systems that have highly parallelized processing units operating on large data sets. The memory channel is contended not only by requests from different user applications (CPU access) but also by system requests for peripheral data (IO access), usually controlled by Direct Memory Access (DMA) engines. Our goal, in this work, is to improve system performance byeliminating memory channel contention between CPU accesses and IO accesses. To this end, we propose a hardware-software cooperative data transfer mechanism, Decoupled DMA (DDMA) that provides a specialized low-cost memory channel for IO accesses. In our DDMA design, main memoryhas two independent data channels, of which one is connected to the processor (CPU channel) and the other to the IO devices (IO channel), enabling CPU and IO accesses to be served on different channels. Systemsoftware or the compiler identifies which requests should be handled on the IO channel and communicates this to the DDMA engine, which then initiates the transfers on the IO channel. By doing so, our proposal increasesthe effective memory channel bandwidth, thereby either accelerating data transfers between system components, or providing opportunities to employ IO performance enhancement techniques (e.g., aggressive IO prefetching)without interfering with CPU accessesWe demonstrate the effectiveness of our DDMA framework in two scenarios: (i) CPU-GPU communication and (ii) in-memory communication (bulk datacopy/initialization within the main memory). By effectively decoupling accesses for CPU-GPU communication and in-memory communication from CPU accesses, our DDMA-based design achieves significant performanceimprovement across a wide variety of system configurations (e.g., 20% average performance improvement on a typical 2-channel 2-rank memory system).","PeriodicalId":385398,"journal":{"name":"2015 International Conference on Parallel Architecture and Compilation (PACT)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124304905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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