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Austin Clements authored
Currently we remove stack barriers during STW mark termination, which has a non-trivial per-goroutine cost and means that we have to touch even clean stacks during mark termination. However, there's no problem with leaving them in during the sweep phase. They just have to be out by the time we install new stack barriers immediately prior to scanning the stack such as during the mark phase of the next GC cycle or during mark termination in a STW GC. Hence, move the gcRemoveStackBarriers from STW mark termination to just before we install new stack barriers during concurrent mark. This removes the cost from STW. Furthermore, this combined with concurrent stack shrinking means that the mark termination scan of a clean stack is a complete no-op, which will make it possible to skip clean stacks entirely during mark termination. This has the downside that it will mess up anything outside of Go that tries to walk Go stacks all the time instead of just some of the time. This includes tools like GDB, perf, and VTune. We'll improve the situation shortly. Change-Id: Ia40baad8f8c16aeefac05425e00b0cf478137097 Reviewed-on: https://go-review.googlesource.com/20667Reviewed-by:
Rick Hudson <rlh@golang.org> Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
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