An Evaluation of Delayed Consistency Protocols

该研究涉及大规模基于缓存的多处理器延迟一致性的实验分析，包括延迟一致性对错误共享和延迟容忍的影响。伪共享是指在并行计算中没有数据共享的情况下，高速缓存块的读/写共享。延迟容限是指通过将共享内存访问与计算重叠来减少它们的平均延迟。延迟一致性利用了基于缓存的系统中的弱排序。高速缓存无效的发送可以被延迟，在这种情况下，它们可能与处理器对高速缓存的访问重叠。此外，无效的发送和接收都可以被延迟，在这种情况下，通过增加高速缓存的块保持可由每个本地处理器访问的时间来减少错误共享效应。延迟一致性及其变体的量化效果将通过并行基准程序的执行驱动模拟来评估，这些并行基准程序包括9个并行数值和非数值算法以及Perfect Club基准套件中包含的13个Fortran程序，该套件使用Alliant 2800编译器进行并行化。重点放在块大小、缓存大小和并行粒度的影响上。统计数据不仅将收集错失率，还将收集内存流量、内存访问延迟和总执行时间的统计数据。

This research involves the experimental analysis of delayed consistency in large-scale cache-based multiprocessors including its effects on false sharing and latency tolerance. False sharing refers to the read/write sharing of cache blocks in the absence of data sharing in a parallel computation. Latency tolerance refers to the reduction of the average latency of shared-memory accesses by overlapping them with computation. Delayed consistency takes advantage of weak ordering in cache-based systems. The sending of cache invalidation can be delayed, in which case they can be overlapped with processor accesses to the cache. Additionally, both the sending and receiving of invalidations can be delayed, in which case false sharing effects are reduced by increasing the time during which cached blocks remain accessible by each local processor. The quantitative effects of delaying consistency and its variants will be evaluated through execution-driven simulation of parallel benchmark programs, including nine parallel numerical as well as non-numerical algorithms and thirteen Fortran programs contained in the Perfect Club Benchmark suite, parallelized using an Alliant 2800 compiler. Emphasis will be on the effects of block size, cache size, and granularity of parallelism. Statistics will be collected not only on miss rates, but also on memory traffic, on memory access latencies and on total execution times.