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go/token: make mutex locking in unpack cheaper

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I was profiling the cpu usage of go/printer's only benchmark,
and found that token.File.Unpack was one of the top offenders.

It was mainly the deferred unlock that took a big chunk of time,
and to my surprise, reoving the use of defer helped significantly:

	name      old time/op    new time/op    delta
	Print-16    5.61ms ± 2%    5.38ms ± 1%  -4.04%  (p=0.000 n=10+8)

	name      old speed      new speed      delta
	Print-16  9.27MB/s ± 2%  9.64MB/s ± 1%  +4.03%  (p=0.000 n=9+8)

	name      old alloc/op   new alloc/op   delta
	Print-16     332kB ± 0%     332kB ± 0%    ~     (p=0.363 n=10+10)

	name      old allocs/op  new allocs/op  delta
	Print-16     3.45k ± 0%     3.45k ± 0%    ~     (all equal)

It seems like #38471 is to blame, as the defer prevents Unlock from
being inlined. Add a TODO as a reminder to come back here once the
compiler issue is fixed.

Change-Id: I5a1c6d36a8e8357435a305a1bc0970ee0358b08a
Reviewed-on: https://go-review.googlesource.com/c/go/+/424920
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Daniel Martí 2022-08-19 10:24:08 +01:00
parent fc34fdb415
commit bdecfcb5fc
1 changed files with 3 additions and 1 deletions
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4
src/go/token/position.go
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@ -286,7 +286,6 @@ func searchLineInfos(a []lineInfo, x int) int {
// possibly adjusted by //line comments; otherwise those comments are ignored.
func (f *File) unpack(offset int, adjusted bool) (filename string, line, column int) {
f.mutex.Lock()
defer f.mutex.Unlock()
filename = f.name
if i := searchInts(f.lines, offset); i >= 0 {
line, column = i+1, offset-f.lines[i]+1
@ -314,6 +313,9 @@ func (f *File) unpack(offset int, adjusted bool) (filename string, line, column
}
}
}
// TODO(mvdan): move Unlock back under Lock with a defer statement once
// https://go.dev/issue/38471 is fixed to remove the performance penalty.
f.mutex.Unlock()
return
}