Simulation study of memory performance of SMP multiprocessors running a TPC-W workload

The infrastructure to support Electronic Commerce is one of the areas where more processing power is currently needed. A multiprocessor system can offer advantages for running Electronic Commerce applications. DAIn this paper C the memory performance of an Electronic Commerce server C i.e. a system running Electronic Commerce applications C is evaluated in the case of shared-bus multiprocessor architecture. The software architecture of this server is based on a three-tier model and the workloads have been setup as specified by the TPC-W benchmark. The hardware configurations are A i 9 a single SMP running tiers two and three and ii 9 two SMPs each one running a single tier.DAWe analyze the influence of memory subsystem on performance and scalability and we consider several solutions aimed at reducing the latency of memory. After initial experiments C which validate our methodology C we explored different choices as for cache C scheduling algorithm C and coherence protocol to enhance performance and scalability. DAAs in previous studies on shared-bus multiprocessors C we found that the memory performance is highly influenced by cache parameters. While scaling the machine C the coherence overhead weighs more and more on the memory performance. False sharing in the kernel is among the main causes of this overhead.DAUnlike previous studies C we were able to highlight that passive sharing - the useless sharing of the private data of the migrating processes - is another important factor that influences the performance. This is especially true when multiprocessors with a higher number of processors are considered A an increase in the number of processors produces real benefits C only if advanced techniques for reducing the coherence overhead are properly adopted.DAScheduling techniques limiting the process migration may reduce passive sharing C while restructuring techniques of the kernel data may reduce false sharing misses. However C even when process migration is reduced through cache-affinity techniques C standard coherence protocols like MESI protocol don 2 0 9t allow for the best performance. Coherence protocols like PSCR and AMSD produce performance benefits. PSCR C in particular C eliminates coherence overhead due to passive sharing and minimizes the number of coherence misses. The adoption of PSCR and cache-affinity scheduling allows us to extend the multiprocessor scalability up to 20 processors for a 128-bit shared-bus and current values of main memory to processor speed gap.