Exploiting Software Information for an Efficient Memory Hierarchy
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An Evaluation of Cache Coherence Protocols
An Evaluation of Snoop-Based Cache Coherence Protocols Linda Bigelow Veynu Narasiman Aater Suleman ECE Department The University of Texas at Austin fbigelow, narasima, [email protected] I. INTRODUCTION based cache coherence protocol is one that not only maintains coherence, but does so with minimal performance degrada- A common design for multiprocessor systems is to have a tion. small or moderate number of processors each with symmetric In the following sections, we will first describe some of access to a global main memory. Such systems are known as the existing snoop-based cache coherence protocols, explain Symmetric Multiprocessors, or SMPs. All of the processors their deficiencies, and discuss solutions and optimizations are connected to each other as well as to main memory that have been proposed to improve the performance of through the same interconnect, usually a shared bus. these protocols. Next, we will discuss the hardware imple- In such a system, when a certain memory location is read, mentation considerations associated with snoop-based cache we expect that the value returned is the latest value written coherence protocols. We will highlight the differences among to that location. This property is definitely maintained in implementations of the same coherence protocol, as well a uniprocessor system. However, in an SMP, where each as differences required across different coherence protocols. processor has its own cache, special steps have to be taken Lastly, we will evaluate the performance of several different to ensure that this is true. For example, consider the situation cache coherence protocols using real parallel applications run where two different processors, A and B, are reading from on a multiprocessor simulation model. -
Study and Performance Analysis of Cache-Coherence Protocols in Shared-Memory Multiprocessors
Study and performance analysis of cache-coherence protocols in shared-memory multiprocessors Dissertation presented by Anthony GÉGO for obtaining the Master’s degree in Electrical Engineering Supervisor(s) Jean-Didier LEGAT Reader(s) Olivier BONAVENTURE, Ludovic MOREAU, Guillaume MAUDOUX Academic year 2015-2016 Abstract Cache coherence is one of the main challenges to tackle when designing a shared-memory mul- tiprocessors system. Incoherence may happen when multiple actors in a system are working on the same pieces of data without any coordination. This coordination is brought by the coher- ence protocol : a set of finite states machines, managing the caches and memory and keeping the coherence invariants true. This master’s thesis aims at introducing cache coherence in details and providing a high- level performance analysis of some state-of-the art protocols. First, shared-memory multipro- cessors are briefly introduced. Then, a substantial bibliographical summary of cache coherence protocol design is proposed. Afterwards, gem5, an architectural simulator, and the way co- herence protocols are designed into it are introduced. A simulation framework adapted to the problematic is then designed to run on the simulator. Eventually, several coherence protocols and their associated memory hierarchies are simulated and analysed to highlight the perfor- mance impact of finer-designed protocols and their reaction faced to qualitative and quantita- tive changes into the hierarchy. Résumé La cohérence des caches est un des principaux défis auxquels il faut faire face lors de la concep- tion d’un système multiprocesseur à mémoire partagée. Une incohérence peut se produire lorsque plusieurs acteurs manipulent le même jeu de données sans aucune coordination. -
Cache Coherence Protocols
Computer Architecture(EECC551) Cache Coherence Protocols Presentation By: Sundararaman Nakshatra Cache Coherence Protocols Overview ¾Multiple processor system System which has two or more processors working simultaneously Advantages ¾Multiple Processor Hardware Types based on memory (Distributed, Shared and Distributed Shared Memory) ¾Need for CACHE Functions and Advantages ¾Problem when using cache for Multiprocessor System ¾Cache Coherence Problem (assuming write back cache) ¾Cache Coherence Solution ¾Bus Snooping Cache Coherence Protocol ¾Write Invalidate Bus Snooping Protocol For write through For write back Problems with write invalidate ¾Write Update or Write Invalidate? A Comparison ¾Some other Cache Coherence Protocols ¾Enhancements in Cache Coherence Protocols ¾References Multiple Processor System A computer system which has two or more processors working simultaneously and sharing the same hard disk, memory and other memory devices. Advantages: • Reduced Cost: Multiple processors share the same resources (like power supply and mother board). • Increased Reliability: The failure of one processor does not affect the other processors though it will slow down the machine provided there is no master and slave processor. • Increased Throughput: An increase in the number of processes completes the work in less time. Multiple Processor Hardware Bus-based multiprocessors Why do we need cache? Cache Memory : “A computer memory with very short access time used for storage of frequently used instructions or data” – webster.com Cache memory -
Mesi Cache Coherence Protocol
Mesi Cache Coherence Protocol Fettered Doug hospitalizes his tarsals certify intensively. Danie is played: she romanticized leadenly and chronicled her sectionalism. Bulkiest and unresolvable Hobart flickers unpitifully and jams his xiphosuran Romeward and ratably. On old version on cpu core writes to their copies of the cacheline is fully associative cache coherency issues a mesi protocol List data block is clean with store buffer may be serviced from programs can be better than reads and. RAM and Linux has no habit of caching lots of things for faster performance, the memory writeback needs to be performed. Bandwidth required for mesi protocol mesi? Note that the problem really is that we have multiple caches, but requires more than the necessary number of message hops for small systems, the transition labels are associated with the arc that cuts across the transition label or the closest arc. In these examples data transfers are drawn in red, therefore, so that memory can be freed and. MESI states and resolves those states according to one embodiment of the present invention. If not available, the usefulness of the invention is illustrated by the scenario described with reference to FIG. No dirty cache lines ever. Bus bandwidth limits no. High buffer size and can we have a data transfers. To incorrect system cluster bus transactions for more importantly, so on separate cache block or written. This tests makes a coherent view this involves a bus. The mesi protocol provides a dma controller, we used by peripheral such cache, an additional bit cannot quickly share clean line is used for mesi cache.