What is the cost of weak determinism?

Abstract

We analyze the fundamental performance impact of enforcing a fixed order of synchronization operations to achieve weak deterministic execution. Our analysis is in three parts, performed on a real system using the SPLASH-2 and PAR-SEC benchmarks. First, we quantify the impact of various sources of nondeterminism on execution of data-race-free programs. We find that thread synchronization is the prevalent source of nondeterminism, sometimes affecting program output. Second, we divorce the implementation overhead of a system imposing a specific synchronization order from the impact of enforcing this order. We show that this fundamental cost of determinism is small (slowdown of 4% on average and 32% in the worst case) and we identify application characteristics responsible for this cost. Finally, we evaluate this cost under perturbed execution conditions. We find that demanding determinism when threads face such conditions can cause almost 2× slowdown.