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I really wish he'd listed all the flags he used. To add on to the flags already listed by some other commenters, `-mcpu` and related flags are really crucial in
by JackYoustra 2y ago
I really wish he'd listed all the flags he used. To add on to the flags already listed by some other commenters, `-mcpu` and related flags are really crucial in these microbenchmarks: over such a small change and such a small set of tight loops, you could just be regression on coincidences in the microarchitecture scheduler vs higher level assumptions.
- j_not_j 2y agoAnd he didn't repeat each test case 5 or 9 times, and take the median (or even an average). There will be operating system noise that can be in the multi-percent range. This is defined as various OS services that run "in the background" taking up cpu time, emptying cache lines (which may be most important), and flushing a few translate lookaside entries. Once you recognize the variability from run to run, claiming "1%" becomes less credible. Depending on the noise level, of course. Linux benchmarks like SPECcpu tend to be run in "single-user mode" meaning almost no background processes are running.