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runtime: track the amount of scannable allocated stack for the GC pacer

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This change adds two fields to gcControllerState: stackScan, used for
pacing decisions, and scannableStackSize, which directly tracks the
amount of space allocated for inuse stacks that will be scanned.

scannableStackSize is not updated directly, but is instead flushed from
each P when at an least 8 KiB delta has accumulated. This helps reduce
issues with atomics contention for newly created goroutines. Stack
growth paths are largely unaffected.

StackGrowth-48			51.4ns ± 0%	51.4ns ± 0%	~	(p=0.927 n=10+10)
StackGrowthDeep-48		6.14µs ± 3%	6.25µs ± 4%	~	(p=0.090 n=10+9)
CreateGoroutines-48		273ns ± 1%	273ns ± 1%	~	(p=0.676 n=9+10)
CreateGoroutinesParallel-48	65.5ns ± 5%	66.6ns ± 7%	~	(p=0.340 n=9+9)
CreateGoroutinesCapture-48	2.06µs ± 1%	2.07µs ± 4%	~	(p=0.217 n=10+10)
CreateGoroutinesSingle-48	550ns ± 3%	563ns ± 4%	+2.41%	(p=0.034 n=8+10)

For #44167.

Change-Id: Id1800d41d3a6c211b43aeb5681c57c0dc8880daf
Reviewed-on: https://go-review.googlesource.com/c/go/+/309589
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Michael Anthony Knyszek 2021-04-12 22:33:54 +00:00 • committed by Michael Knyszek
parent 8e112a7c2a
commit 9ac1ee2d46
4 changed files with 45 additions and 2 deletions
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5
src/runtime/stack.go
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@ -852,6 +852,11 @@ func copystack(gp *g, newsize uintptr) {
throw("nil stackbase")
}
used := old.hi - gp.sched.sp
// Add just the difference to gcController.addScannableStack.
// g0 stacks never move, so this will never account for them.
// It's also fine if we have no P, addScannableStack can deal with
// that case.
gcController.addScannableStack(getg().m.p.ptr(), int64(newsize)-int64(old.hi-old.lo))
// allocate new stack
new := stackalloc(uint32(newsize))