ea0386f85f
During random stealing we steal 4*GOMAXPROCS times from random procs. One would expect that most of the time we check all procs this way, but due to low quality PRNG we actually miss procs with frightening probability. Below are modelling experiment results for 1e6 tries: GOMAXPROCS = 2 : missed 1 procs 7944 times GOMAXPROCS = 3 : missed 1 procs 101620 times GOMAXPROCS = 3 : missed 2 procs 3571 times GOMAXPROCS = 4 : missed 1 procs 63916 times GOMAXPROCS = 4 : missed 2 procs 61 times GOMAXPROCS = 4 : missed 3 procs 16 times GOMAXPROCS = 5 : missed 1 procs 133136 times GOMAXPROCS = 5 : missed 2 procs 1025 times GOMAXPROCS = 5 : missed 3 procs 101 times GOMAXPROCS = 5 : missed 4 procs 15 times GOMAXPROCS = 8 : missed 1 procs 151765 times GOMAXPROCS = 8 : missed 2 procs 5057 times GOMAXPROCS = 8 : missed 3 procs 1726 times GOMAXPROCS = 8 : missed 4 procs 68 times GOMAXPROCS = 12 : missed 1 procs 199081 times GOMAXPROCS = 12 : missed 2 procs 27489 times GOMAXPROCS = 12 : missed 3 procs 3113 times GOMAXPROCS = 12 : missed 4 procs 233 times GOMAXPROCS = 12 : missed 5 procs 9 times GOMAXPROCS = 16 : missed 1 procs 237477 times GOMAXPROCS = 16 : missed 2 procs 30037 times GOMAXPROCS = 16 : missed 3 procs 9466 times GOMAXPROCS = 16 : missed 4 procs 1334 times GOMAXPROCS = 16 : missed 5 procs 192 times GOMAXPROCS = 16 : missed 6 procs 5 times GOMAXPROCS = 16 : missed 7 procs 1 times GOMAXPROCS = 16 : missed 8 procs 1 times A missed proc won't lead to underutilization because we check all procs again after dropping P. But it can lead to an unpleasant situation when we miss a proc, drop P, check all procs, discover work, acquire P, miss the proc again, repeat. Improve stealing logic to cover all procs. Also don't enter spinning mode and try to steal when there is nobody around. Change-Id: Ibb6b122cc7fb836991bad7d0639b77c807aab4c2 Reviewed-on: https://go-review.googlesource.com/20836 Reviewed-by: Rick Hudson <rlh@golang.org> Run-TryBot: Dmitry Vyukov <dvyukov@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com> |
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