nikic added a comment. In D128439#3607289 <https://reviews.llvm.org/D128439#3607289>, @mboehme wrote:
> Just a question for my understanding before I abandon the change: Shouldn't > the "instructions" count be relatively resistant to noise? (I was assuming > this is based on performance counters? What would cause noise in this metric?) There are two primary sources of noise. The first is kernel activity, as the `instructions` metric is a combined userspace and kernel metric. I do collect userspace-only as well (this is `instructions:u`). On that metric this does look like a small improvement just above the noise floor: http://llvm-compile-time-tracker.com/compare.php?from=8b6f69a4da5baaf3748798a84dd16a2481b7ca7f&to=797ba50f5fd88017925fe765427b1f5f136c3310&stat=instructions:u The other is ASLR. If ASLR is disabled, the `instructions:u` measurements become perfectly noise-free. This is actually bad, because a lot of changes will then show statistically significant and perfectly reproducible compile-time changes that are ultimately just down to how exactly the address space gets laid out. So this is intentional noise :) And yes, execution statistics are collected using `perf`. `callgrind` uses a CPU simulator instead, which is a much more controlled environment... Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D128439/new/ https://reviews.llvm.org/D128439 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
