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runtime/pprof: assert that labelHog samples are always labeled

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With https://golang.org/issue/50007 resolved, there are no known issues
with pprof labels remaining. Thus, the 10% allowed error in
TestLabelSystemstack should not be required.

Drop it in favor of an explicit assertion that all samples containing
labelHog are properly labeled.

This is no flaky in my local testing. It is possible that other bugs
will appear at larger testing scale, in which case this CL will be
reverted, but then at least we will be aware of additional failure
modes.

For #50007.

Change-Id: I1ef530c303bd9a01af649b8b08d4b35505e8aada
Reviewed-on: https://go-review.googlesource.com/c/go/+/369744
Reviewed-by: Bryan Mills <bcmills@google.com>
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Michael Pratt 2021-12-06 17:26:32 -05:00
parent a3ae45ebe1
commit 0a15e7851a
1 changed files with 22 additions and 46 deletions
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68
src/runtime/pprof/pprof_test.go
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@ -1425,52 +1425,8 @@ func TestLabelRace(t *testing.T) {
// TestLabelSystemstack makes sure CPU profiler samples of goroutines running
// on systemstack include the correct pprof labels. See issue #48577
func TestLabelSystemstack(t *testing.T) {
matchBasics := matchAndAvoidStacks(stackContainsLabeled, []string{"runtime.systemstack;key=value"}, avoidFunctions())
matches := func(t *testing.T, prof *profile.Profile) bool {
if !matchBasics(t, prof) {
return false
}
var withLabel, withoutLabel int64
for _, s := range prof.Sample {
var systemstack, labelHog bool
for _, loc := range s.Location {
for _, l := range loc.Line {
switch l.Function.Name {
case "runtime.systemstack":
systemstack = true
case "runtime/pprof.labelHog":
labelHog = true
}
}
}
if systemstack && labelHog {
if s.Label != nil && contains(s.Label["key"], "value") {
withLabel += s.Value[0]
} else {
withoutLabel += s.Value[0]
}
}
}
// ratio on 2019 Intel MBP before/after CL 351751 for n=30 runs:
// before: mean=0.013 stddev=0.013 min=0.000 max=0.039
// after : mean=0.996 stddev=0.007 min=0.967 max=1.000
//
// TODO: Figure out why some samples (containing gcWriteBarrier, gcStart)
// still have labelHog without labels. Once fixed this test case can be
// simplified to just check that all samples containing labelHog() have the
// label, and no other samples do.
ratio := float64(withLabel) / float64((withLabel + withoutLabel))
if ratio < 0.9 {
t.Logf("only %.1f%% of labelHog(systemstack()) samples have label", ratio*100)
return false
}
return true
}
testCPUProfile(t, matches, func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContainsLabeled, []string{"runtime.systemstack;key=value"}, avoidFunctions())
p := testCPUProfile(t, matches, func(dur time.Duration) {
Do(context.Background(), Labels("key", "value"), func(context.Context) {
var wg sync.WaitGroup
stop := make(chan struct{})
@ -1487,6 +1443,26 @@ func TestLabelSystemstack(t *testing.T) {
wg.Wait()
})
})
// labelHog should always be labeled.
for _, s := range p.Sample {
for _, loc := range s.Location {
for _, l := range loc.Line {
if l.Function.Name != "runtime/pprof.labelHog" {
continue
}
if s.Label == nil {
t.Errorf("labelHog sample labels got nil want key=value")
continue
}
if !contains(s.Label["key"], "value") {
t.Errorf("labelHog sample labels got %+v want contains key=value", s.Label)
continue
}
}
}
}
}
// labelHog is designed to burn CPU time in a way that a high number of CPU