af060c3086
Currently, the entire GC process runs with g.m.preemptoff set. In the concurrent phases, the parts that actually need preemption disabled are run on a system stack and there's no overall need to stay on the same M or P during the concurrent phases. Hence, move the setting of g.m.preemptoff to when we start mark termination, at which point we really do need preemption disabled. This dramatically changes the scheduling behavior of the concurrent mark phase. Currently, since this is non-preemptible, concurrent mark gets one dedicated P (so 1/GOMAXPROCS utilization). With this change, the GC goroutine is scheduled like any other goroutine during concurrent mark, so it gets 1/<runnable goroutines> utilization. You might think it's not even necessary to set g.m.preemptoff at that point since the world is stopped, but stackalloc/stackfree use this as a signal that the per-P pools are not safe to access without synchronization. Change-Id: I08aebe8179a7d304650fb8449ff36262b3771099 Reviewed-on: https://go-review.googlesource.com/8839 Reviewed-by: Rick Hudson <rlh@golang.org> |
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