March 2020: I was planning to write about CPU microarchitecture analysis for a long time. I started writing this post more than a year ago, just before the beginning of COVID-19. But with so many things happening around (and new parenting responsibilities 👧), this got delayed for quite a long time. Finally getting some weekend time to get this out!
When optimizing parallel applications at scale, we often focus on computation-communication aspects and I/O often gets limited attention. With increasing performance gap between compute and I/O subsystems, improving I/O performance remains one of the major challenge. As filesystem is a shared resource, few jobs running on a system can significantly impact performance of other applications. In such scenario, even if we use profiling tool (see list here) to identify slow I/O routines, it's difficult to understand real cause. For example, there might be other applications dominating filesystem resulting in poor I/O performance.… Read the rest