Download or read book Directory Based Ring order Cache Coherence Protocol for Many core Chip Mulitprocessors written by Anup Narayan Kulkarni and published by . This book was released on 2009 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: The success of the current trend of aggressively scaling shared-cache Chip Multi Processors (CMP) depends critically on the ability of hardware cache coherence proto¬cols to support the scaling of processing cores while providing low latency service time for cache misses. Recent research has identified the ring to be a good candidate for on-chip interconnect that supports the scaling of processor cores. An associated ring-order snoop based protocol was proposed for the ring interconnect. However, in general, snoop based protocols do not scale well for a large number of processing cores. In this thesis, we propose a variation of the ring-the hierarchical ring for shared cache CMP's. Addi¬tionally, we develop a new directory based cache coherence protocol that exploits the ring's natural round-robin order while delivering good performance in terms of reduced latency for cache misses by exploiting the shorter routes possible with the hierarchical ring. We present simulation results comparing the performance of the ring-order snoop based protocol on the hierarchical ring against our protocol using a set of synthetic benchmarks. On an average the proposed protocol has 25% lower latency than the snoop based ring-order protocol for a 128 core processor with private LI caches and a logically shared but physically distributed L2 cache.
Download or read book A Primer on Memory Consistency and Cache Coherence written by Daniel Sorin and published by Morgan & Claypool Publishers. This book was released on 2011-03-02 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many modern computer systems and most multicore chips (chip multiprocessors) support shared memory in hardware. In a shared memory system, each of the processor cores may read and write to a single shared address space. For a shared memory machine, the memory consistency model defines the architecturally visible behavior of its memory system. Consistency definitions provide rules about loads and stores (or memory reads and writes) and how they act upon memory. As part of supporting a memory consistency model, many machines also provide cache coherence protocols that ensure that multiple cached copies of data are kept up-to-date. The goal of this primer is to provide readers with a basic understanding of consistency and coherence. This understanding includes both the issues that must be solved as well as a variety of solutions. We present both highlevel concepts as well as specific, concrete examples from real-world systems. Table of Contents: Preface / Introduction to Consistency and Coherence / Coherence Basics / Memory Consistency Motivation and Sequential Consistency / Total Store Order and the x86 Memory Model / Relaxed Memory Consistency / Coherence Protocols / Snooping Coherence Protocols / Directory Coherence Protocols / Advanced Topics in Coherence / Author Biographies
Download or read book Cache Coherence Techniques for Multicore Processors written by Michael R. Marty and published by . This book was released on 2008 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Efficient and Scalable Cache Coherence for Chip Multiprocessors written by Alberto Ros and published by LAP Lambert Academic Publishing. This book was released on 2010-02 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chip multiprocessors (CMPs) constitute the new trend for increasing the performance of future computers. In the near future, chips with tens of cores will become more popular. Nowadays, directory-based protocols constitute the best alternative to keep cache coherence in large-scale systems. Nevertheless, directory-based protocols have two important issues that prevent them from achieving better scalability: the directory memory overhead and the long cache miss latencies. This book focuses on these key issues. The first proposal is a scalable distributed directory organization that copes with the memory overhead of directory-based protocols. The second proposal presents the direct coherence protocols, which are aimed at avoiding the indirection problem of traditional directory-based protocols and, therefore, they improve applications' performance. Finally, a novel mapping policy for distributed caches is presented. This policy reduces the long access latency while lessening the number of off-chip accesses, leading to improvements in applications' execution time.
Download or read book Chip Multiprocessor Coherence and Interconnect System Design written by Natalie D. Enright Jerger and published by . This book was released on 2008 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effective On chip Cache Utilization in Chip Multiprocessors written by Hemayet Hossain and published by . This book was released on 2010 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt: "CMOS scaling trends allow increasing numbers of transistors on a single chip but with a limited power budget. Processor designers are increasingly turning toward multicore architectures- often chip multiprocessor (CMP) of simultaneous multithreaded (SMT) cores- in order to leverage these trends. However, increasing the number of cores on a single chip leads to higher demand on the on-chip cache capacity as well as on both on-chip and off-chip bandwidth due to coherence and capacity-related misses, respectively. Cache access latencies are also often a function of distance on the chip. Directory-based cache coherence protocols can support a large number of cores by reducing coherence bandwidth requirements but they introduce a level of indirection on the critical path of cache misses, resulting in increased communication latency depending on where data and coherence information are mapped. Many multithreaded commercial, scientific, and data mining workloads exhibit finegrain (both temporal and spatial) data sharing patterns due to data communication and synchronization. In addition, multiprogrammed and single-threaded applications, while exhibiting limited sharing behavior, may have working sets that well exceed the onchip cache capacity. On-chip caches must therefore adapt to these varying needs in order to reduce L1 miss penalties and both on-chip and off-chip bandwidth needs for all application domains. In this dissertation, we propose and evaluate cache coherence protocols that (1) exploit the low-latency on-chip interconnect to solve the directory-based indirection problem by using prediction to directly access the most up-to-date copy of the data, (2) support fine-grain sharing by localizing communication between the closest sharing nodes, (3) reduce access latency by bringing both data and metadata as close to the accesser as possible, and (4) increase effective cache capacity by reducing the number of copies of data in the caches and using access pattern aware adaptive replacement policies. We show that our techniques are effective at improving cache utilization and at reducing both on- and off-chip traffic and energy consumption. These properties are essential to ensure the continued scaling of future multi-core platforms."--Leaves vi-vii.
Download or read book Locality aware Cache Hierarchy Management for Multicore Processors written by and published by . This book was released on 2015 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Next generation multicore processors and applications will operate on massive data with significant sharing. A major challenge in their implementation is the storage requirement for tracking the sharers of data. The bit overhead for such storage scales quadratically with the number of cores in conventional directory-based cache coherence protocols. Another major challenge is limited cache capacity and the data movement incurred by conventional cache hierarchy organizations when dealing with massive data scales. These two factors impact memory access latency and energy consumption adversely. This thesis proposes scalable efficient mechanisms that improve effective cache capacity (i.e., by improving utilization) and reduce data movement by exploiting locality and controlling replication. First, a limited directory-based protocol, ACKwise is proposed to track the sharers of data in a cost-effective manner. ACKwise leverages broadcasts to implement scalable cache coherence. Broadcast support can be implemented in a 2-D mesh network by making simple changes to its routing policy without requiring any additional virtual channels. Second, a locality-aware replication scheme that better manages the private caches is proposed. This scheme controls replication based on data reuse information and seamlessly adapts between private and logically shared caching of on-chip data at the fine granularity of cache lines. A low-overhead runtime profiling capability to measure the locality of each cache line is built into hardware. Private caching is only allowed for data blocks with high spatio-temporal locality. Third, a Timestamp-based memory ordering validation scheme is proposed that enables the locality-aware private cache replication scheme to be implementable in processors with out-of-order memory that employ popular memory consistency models. This method does not rely on cache coherence messages to detect speculation violations, and hence is applicable to the locality-aware protocol. The timestamp mechanism is efficient due to the observation that consistency violations only occur due to conflicting accesses that have temporal proximity (i.e., within a few cycles of each other), thus requiring timestamps to be stored only for a small time window. Fourth, a locality-aware last-level cache (LLC) replication scheme that better manages the LLC is proposed. This scheme adapts replication at runtime based on fine-grained cache line reuse information and thereby, balances data locality and off-chip miss rate for optimized execution. Finally, all the above schemes are combined to obtain a cache hierarchy replication scheme that provides optimal data locality and miss rates at all levels of the cache hierarchy. The design of this scheme is motivated by the experimental observation that both locality-aware private cache & LLC replication enable varying performance improvements across benchmarks. These techniques enable optimal use of the on-chip cache capacity, and provide low-latency, low-energy memory access, while retaining the convenience of shared memory and preserving the same memory consistency model. On a 64-core multicore processor with out-of-order cores, Locality-aware Cache Hierarchy Replication improves completion time by 15% and energy by 22% over a state-of-the-art baseline while incurring a storage overhead of 30.7 KB per core. (i.e., 10% the aggregate cache capacity of each core).
Download or read book Mobile Home Node written by Tarun Soni and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The implementation of multiple processors on a single chip has been made possible with advancements in process technology. The benefits of having multiple cores on a single chip bring with it a new set of constraints for maintaining fast and consistent memory accesses. Cache coherence protocols are needed to maintain the consistency of shared memory on individual caches. Current cache coherency protocols are either snoop based, which is not scalable but provides fast access for small number of cores, or directory based, which involves a directory that acts as the ordering point providing scalability with relatively slower access. Our focus is on improving the memory access time of the scalable directory protocol. We have observed that most memory requests follow a pattern where in one of the processors, which we will dub the Producer, repeatedly writes to a particular memory location. A subset of the remaining cores, which we will dub the Consumers, repeatedly read the data from that same memory location. In our implementation we utilize this relationship to provide direct cache to cache transfers and minimize the access time by avoiding the indirection through the directory. We move the directory temporarily to the Producer node so that the consumer can directly request the producer for the cache line. Our technique improves the memory access time by 13 percent and reduces network traffic by 30 percent over standard directory coherence protocol with very little area overhead.
Download or read book Cache and Interconnect Architectures in Multiprocessors written by Michel Dubois and published by Springer. This book was released on 1990-07-31 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: A collection of invited papers concerning cache coherence protocols for general interconnects. Covers the major efforts now under way to understand the architecture and performance issues of cache-based multiprocessor computer systems. Annotation copyrighted by Book News, Inc., Portland, OR
Download or read book Proximity Coherence for Chip multiprocessors written by Nick Barrow-Williams and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Many-core architectures provide an efficient way of harnessing the growing numbers of transistors available in modern fabrication processes; however, the parallel programs run on these platforms are increasingly limited by the energy and latency costs of communication. Existing designs provide a functional communication layer but do not necessarily implement the most efficient solution for chip-multiprocessors, placing limits on the performance of these complex systems. In an era of increasingly power limited silicon design, efficiency is now a primary concern that motivates designers to look again at the challenge of cache coherence. The first step in the design process is to analyse the communication behaviour of parallel benchmark suites such as Parsec and SPLASH-2. This thesis presents work detailing the sharing patterns observed when running the full benchmarks on a simulated 32-core x86 machine. The results reveal considerable locality of shared data accesses between threads with consecutive operating system assigned thread IDs. This pattern, although of little consequence in a multi-node system, corresponds to strong physical locality of shared data between adjacent cores on a chip-multiprocessor platform. Traditional cache coherence protocols, although often used in chip-multiprocessor designs, have been developed in the context of older multi-node systems. By redesign- ing coherence protocols to exploit new patterns such as the physical locality of shared data, improving the efficiency of communication, specifically in chip-multiprocessors, is possible. This thesis explores such a design - Proximity Coherence - a novel scheme in which L1 load misses are optimistically forwarded to nearby caches via new dedicated links rather than always being indirected via a directory structure.
Download or read book Lock Based Cache Coherence Protocol for Chip Multiprocessors written by Ihab Hossam Ismail and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Cache Coherence in Multiprocessor Computer Systems Using Memory Based Directories written by Anthony Thomas Laundrie and published by . This book was released on 1990 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Primer on Memory Consistency and Cache Coherence written by Vijay Nagarajan and published by Morgan & Claypool Publishers. This book was released on 2020-02-04 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many modern computer systems, including homogeneous and heterogeneous architectures, support shared memory in hardware. In a shared memory system, each of the processor cores may read and write to a single shared address space. For a shared memory machine, the memory consistency model defines the architecturally visible behavior of its memory system. Consistency definitions provide rules about loads and stores (or memory reads and writes) and how they act upon memory. As part of supporting a memory consistency model, many machines also provide cache coherence protocols that ensure that multiple cached copies of data are kept up-to-date. The goal of this primer is to provide readers with a basic understanding of consistency and coherence. This understanding includes both the issues that must be solved as well as a variety of solutions. We present both high-level concepts as well as specific, concrete examples from real-world systems. This second edition reflects a decade of advancements since the first edition and includes, among other more modest changes, two new chapters: one on consistency and coherence for non-CPU accelerators (with a focus on GPUs) and one that points to formal work and tools on consistency and coherence.
Download or read book Implementing a Directory based Cache Consistency Protocol written by Stanford University. Computer Systems Laboratory and published by . This book was released on 1990 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Directory-based cache consistency protocols have the potential to allow shared-memory multiprocessors to scale to a large number of processors. While many variations of these coherence schemes exist in the literature, they have typically been described at a rather high level, making adequate evaluation difficult. This paper explores the implementation issues of directory-based coherency strategies by developing a design at the level of detail needed to write a memory system functional simulator with an accurate timing model. The paper presents the design of both an invalidation coherency protocol and the associated directory/memory hardware. Support is added to prevent deadlock, handle subtle consistency situations, and implement a proper programming model of multiprocess execution. Extensions are delineated for realizing a multiple-threaded directory that can continue to process commands while waiting for a reply from a cache. The final hardware design is evaluated in the context of the number of parts required for implementation.
Download or read book Parallel Computer Organization and Design written by Michel Dubois and published by Cambridge University Press. This book was released on 2012-08-30 with total page 561 pages. Available in PDF, EPUB and Kindle. Book excerpt: A design-oriented text for advanced computer architecture courses, covering parallelism, complexity, power, reliability and performance.
Download or read book Directory Based Cache Coherency Organization Operations and Challenges in Implementation Study written by Subrahmanya Bhat and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Today's systems are designed with Multi Core Architecture. The idea behind this is to achieve high system throuput. Once the Processor clock speed reached its saturation, designers opted for having multiple cores. Each Core or Processor equipped with their own private cache memory. But under Chip Multiprocessor, where all the processor have access to shared memory, having respective cache memory will result with Cache Coherency Problem. In Directory Protocol, for each block of data there is a directory entry that contains a number of pointers. The purpose of this number is to mention the locations of block copies. The important advantage of directory based protocols is that they scale much better than snoopy protocols. In addition to this it has the advantage of ability to exploit arbitrary point-to-point interconnects. But mean time it also has the overhead in terms of the storage and manipulation of directory state. This paper discus different Directory Based implementation, operations along with and its implementation difficulties.
Download or read book Synchronization in Timestamp based Cache Coherence Protocols written by Quan Minh Nguyen (S.M.) and published by . This book was released on 2016 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: Supporting computationally demanding workloads into the future requires that multiprocessor systems support hundreds or thousands of cores. A cache coherence protocol manages the memory cached by these many cores, but the storage overhead required by existing directory-based protocols to track coherence state scales poorly as the number of cores increases. The Tardis cache coherence protocol uses timestamps to avoid these scalability problems. We build a cycle-level multicore simulator that implements a version of the Tardis protocol that uses release consistency. Changing the coherence protocol, which affects what memory values a processor can observe, changes inter-processor communication and synchronization, two processes crucial to the operation of a multicore system. We construct Tardis versions of synchronization primitives and the atomic instructions they use, and compare them to their analogous implementations on a directory-based cache coherent multicore system. Simulations on several benchmarks suggest that the Tardis system performs just as well as the baseline system while preserving the ability to scale systems to hundreds or thousands of cores.
