4b956ae317
Currently, when allocation reaches the concurrent GC trigger size, we start the concurrent collector by ready'ing its G. This simply puts it on the end of the P's run queue, which means we may not actually start GC for some time as the current G continues to run and then the P drains other Gs already on its run queue. Since the mutator can continue to allocate, the heap can potentially be much larger than we intended by the time GC actually starts. Furthermore, how much larger is difficult to predict since it depends on the scheduler. Fix this by preempting the current G and switching directly to the concurrent GC G as soon as we reach the trigger heap size. On the garbage benchmark from the benchmarks subrepo with GOMAXPROCS=4, this reduces the time from triggering the GC to the beginning of sweep termination by 10 to 30 milliseconds, which reduces allocation after the trigger by up to 10MB (a large fraction of the 64MB live heap the benchmark tries to maintain). One other known source of delay before we "really" start GC is the sweep finalization performed before sweep termination. This has similar negative effects on heap size and predictability, but is an orthogonal problem. This change adds a TODO for this. Change-Id: I8bae98cb43685c1bf353ff55868e4647e3743c47 Reviewed-on: https://go-review.googlesource.com/8513 Reviewed-by: Rick Hudson <rlh@golang.org> |
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