89b7a08aea
The CPU time reported in the gctrace for STW phases is simply work.stwprocs times the wall-clock duration of these phases. However, work.stwprocs is set to gcprocs(), which is wrong for multiple reasons: 1. gcprocs is intended to limit the number of Ms used for mark termination based on how well the garbage collector actually scales, but the gctrace wants to report how much CPU time is being stolen from the application. During STW, that's *all* of the CPU, regardless of how many the garbage collector can actually use. 2. gcprocs assumes it's being called during STW, so it limits its result to sched.nmidle+1. However, we're not calling it during STW, so sched.nmidle is typically quite small, even if GOMAXPROCS is quite large. Fix this by setting work.stwprocs to min(ncpu, GOMAXPROCS). This also fixes the overall GC CPU fraction, which is based on the computed CPU times. Fixes #22725. Change-Id: I64b5ce87e28dbec6870aa068ce7aecdd28c058d1 Reviewed-on: https://go-review.googlesource.com/77710 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org>
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