Evaluating Candidate Instructions for Reliable Program Slowdown at the Compiler Level

Slowing down programs has surprisingly many use cases: it helps finding race conditions, enables speedup estimation, and allows us to assess a profiler’s accuracy. Yet, slowing down a program is complicated because today’s CPUs and runtime systems can optimize execution on the fly, making it challenging to preserve a program’s performance behavior to avoid introducing bias. We evaluate six x86 instruction candidates for controlled and fine-grained slowdown including NOP, MOV, and PAUSE. We tested each candidate’s ability to achieve an overhead of 100%, to maintain the profiler-observable performance behavior, and whether slowdown placement within basic blocks influences results. On an Intel Core i5-10600, our ex- periments suggest that only NOP and MOV instructions are suit- able. We believe these experiments can guide future research on advanced developer tooling that utilizes fine-granular slowdown at the machine-code level.