On the memory system requirements of future scientific applications: Four case-studies

In this paper, we observe and characterize the memory behaviour, and specifically memory footprint, memory bandwidth and cache effectiveness, of several well-known parallel scientific applications running on a large processor cluster. Based on the analysis of their instrumented execution, we project some performance requirements from future memory systems serving large-scale chip multiprocessors (CMPs). In addition, we estimate the impact of memory system performance on the amount of instruction stalls, as well as on the real computational performance, using the number of floating point operations per second the applications perform. Our projections show that the limitations of present memory technologies, either by means of capacity or bandwidth, will have a strong negative impact on scalability of memory systems for large CMPs. We conclude that future supercomputer systems require research on new alternative memory architectures, capable of offering both capacity and bandwidth beyond what current solutions provide.