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runtime: fix missing pprof labels

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Use gp.m.curg instead of the gp when recording cpu profiler stack
traces. This ensures profiler labels are captured when systemstack or similar
is executing on behalf of the current goroutine.

After this there are still rare cases of samples containing the labelHog
function, so more work might be needed. This patch should fix ~99% of the
problem.

Also change testCPUProfile interface a little to allow the new test to
re-run with a longer duration if it fails during a -short run.

Fixes #48577.

Change-Id: I3dbc9fd5af3c513544e822acaa43055b2e00dfa9
Reviewed-on: https://go-review.googlesource.com/c/go/+/367200
Trust: Michael Pratt <mpratt@google.com>
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Felix Geisendörfer 2021-09-20 16:09:47 +02:00 committed by Michael Pratt
parent a174638a5c
commit 9b0de0854d
3 changed files with 178 additions and 71 deletions
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11
src/runtime/cpuprof.go
View File

@ -89,7 +89,7 @@ func SetCPUProfileRate(hz int) {
// held at the time of the signal, nor can it use substantial amounts
// of stack.
//go:nowritebarrierrec
func (p *cpuProfile) add(gp *g, stk []uintptr) {
func (p *cpuProfile) add(tagPtr *unsafe.Pointer, stk []uintptr) {
// Simple cas-lock to coordinate with setcpuprofilerate.
for !atomic.Cas(&prof.signalLock, 0, 1) {
osyield()
@ -104,15 +104,6 @@ func (p *cpuProfile) add(gp *g, stk []uintptr) {
// because otherwise its write barrier behavior may not
// be correct. See the long comment there before
// changing the argument here.
//
// Note: it can happen on Windows, where we are calling
// p.add with a gp that is not the current g, that gp is nil,
// meaning we interrupted a system thread with no g.
// Avoid faulting in that case.
var tagPtr *unsafe.Pointer
if gp != nil {
tagPtr = &gp.labels
}
cpuprof.log.write(tagPtr, nanotime(), hdr[:], stk)
}

177
src/runtime/pprof/pprof_test.go
View File

@ -93,14 +93,16 @@ func avoidFunctions() []string {
}
func TestCPUProfile(t *testing.T) {
testCPUProfile(t, stackContains, []string{"runtime/pprof.cpuHog1"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"runtime/pprof.cpuHog1"}, avoidFunctions())
testCPUProfile(t, matches, func(dur time.Duration) {
cpuHogger(cpuHog1, &salt1, dur)
})
}
func TestCPUProfileMultithreaded(t *testing.T) {
defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
testCPUProfile(t, stackContains, []string{"runtime/pprof.cpuHog1", "runtime/pprof.cpuHog2"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"runtime/pprof.cpuHog1", "runtime/pprof.cpuHog2"}, avoidFunctions())
testCPUProfile(t, matches, func(dur time.Duration) {
c := make(chan int)
go func() {
cpuHogger(cpuHog1, &salt1, dur)
@ -167,7 +169,8 @@ func TestCPUProfileMultithreadMagnitude(t *testing.T) {
runtime.GC()
var cpuTime1, cpuTimeN time.Duration
p := testCPUProfile(t, stackContains, []string{"runtime/pprof.cpuHog1", "runtime/pprof.cpuHog3"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"runtime/pprof.cpuHog1", "runtime/pprof.cpuHog3"}, avoidFunctions())
p := testCPUProfile(t, matches, func(dur time.Duration) {
cpuTime1 = diffCPUTime(t, func() {
// Consume CPU in one goroutine
cpuHogger(cpuHog1, &salt1, dur)
@ -272,7 +275,8 @@ func TestCPUProfileInlining(t *testing.T) {
t.Skip("Can't determine whether inlinedCallee was inlined into inlinedCaller.")
}
p := testCPUProfile(t, stackContains, []string{"runtime/pprof.inlinedCallee", "runtime/pprof.inlinedCaller"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"runtime/pprof.inlinedCallee", "runtime/pprof.inlinedCaller"}, avoidFunctions())
p := testCPUProfile(t, matches, func(dur time.Duration) {
cpuHogger(inlinedCaller, &salt1, dur)
})
@ -322,7 +326,8 @@ func inlinedCalleeDump(pcs []uintptr) {
}
func TestCPUProfileRecursion(t *testing.T) {
p := testCPUProfile(t, stackContains, []string{"runtime/pprof.inlinedCallee", "runtime/pprof.recursionCallee", "runtime/pprof.recursionCaller"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"runtime/pprof.inlinedCallee", "runtime/pprof.recursionCallee", "runtime/pprof.recursionCaller"}, avoidFunctions())
p := testCPUProfile(t, matches, func(dur time.Duration) {
cpuHogger(recursionCaller, &salt1, dur)
})
@ -407,7 +412,7 @@ func cpuProfilingBroken() bool {
// testCPUProfile runs f under the CPU profiler, checking for some conditions specified by need,
// as interpreted by matches, and returns the parsed profile.
func testCPUProfile(t *testing.T, matches matchFunc, need []string, avoid []string, f func(dur time.Duration)) *profile.Profile {
func testCPUProfile(t *testing.T, matches profileMatchFunc, f func(dur time.Duration)) *profile.Profile {
switch runtime.GOOS {
case "darwin":
out, err := exec.Command("uname", "-a").CombinedOutput()
@ -448,7 +453,7 @@ func testCPUProfile(t *testing.T, matches matchFunc, need []string, avoid []stri
f(duration)
StopCPUProfile()
if p, ok := profileOk(t, matches, need, avoid, prof, duration); ok {
if p, ok := profileOk(t, matches, prof, duration); ok {
return p
}
@ -504,15 +509,11 @@ func stackContains(spec string, count uintptr, stk []*profile.Location, labels m
return false
}
type matchFunc func(spec string, count uintptr, stk []*profile.Location, labels map[string][]string) bool
type sampleMatchFunc func(spec string, count uintptr, stk []*profile.Location, labels map[string][]string) bool
func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, prof bytes.Buffer, duration time.Duration) (_ *profile.Profile, ok bool) {
func profileOk(t *testing.T, matches profileMatchFunc, prof bytes.Buffer, duration time.Duration) (_ *profile.Profile, ok bool) {
ok = true
// Check that profile is well formed, contains 'need', and does not contain
// anything from 'avoid'.
have := make([]uintptr, len(need))
avoidSamples := make([]uintptr, len(avoid))
var samples uintptr
var buf bytes.Buffer
p := parseProfile(t, prof.Bytes(), func(count uintptr, stk []*profile.Location, labels map[string][]string) {
@ -520,20 +521,6 @@ func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, p
fprintStack(&buf, stk)
fmt.Fprintf(&buf, " labels: %v\n", labels)
samples += count
for i, spec := range need {
if matches(spec, count, stk, labels) {
have[i] += count
}
}
for i, name := range avoid {
for _, loc := range stk {
for _, line := range loc.Line {
if strings.Contains(line.Function.Name, name) {
avoidSamples[i] += count
}
}
}
}
fmt.Fprintf(&buf, "\n")
})
t.Logf("total %d CPU profile samples collected:\n%s", samples, buf.String())
@ -556,6 +543,42 @@ func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, p
ok = false
}
if matches != nil && !matches(t, p) {
ok = false
}
return p, ok
}
type profileMatchFunc func(*testing.T, *profile.Profile) bool
func matchAndAvoidStacks(matches sampleMatchFunc, need []string, avoid []string) profileMatchFunc {
return func(t *testing.T, p *profile.Profile) (ok bool) {
ok = true
// Check that profile is well formed, contains 'need', and does not contain
// anything from 'avoid'.
have := make([]uintptr, len(need))
avoidSamples := make([]uintptr, len(avoid))
for _, sample := range p.Sample {
count := uintptr(sample.Value[0])
for i, spec := range need {
if matches(spec, count, sample.Location, sample.Label) {
have[i] += count
}
}
for i, name := range avoid {
for _, loc := range sample.Location {
for _, line := range loc.Line {
if strings.Contains(line.Function.Name, name) {
avoidSamples[i] += count
}
}
}
}
}
for i, name := range avoid {
bad := avoidSamples[i]
if bad != 0 {
@ -565,7 +588,7 @@ func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, p
}
if len(need) == 0 {
return p, ok
return
}
var total uintptr
@ -577,6 +600,7 @@ func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, p
t.Logf("no samples in expected functions")
ok = false
}
// We'd like to check a reasonable minimum, like
// total / len(have) / smallconstant, but this test is
// pretty flaky (see bug 7095). So we'll just test to
@ -588,7 +612,8 @@ func profileOk(t *testing.T, matches matchFunc, need []string, avoid []string, p
ok = false
}
}
return p, ok
return
}
}
// Fork can hang if preempted with signals frequently enough (see issue 5517).
@ -704,7 +729,7 @@ func fprintStack(w io.Writer, stk []*profile.Location) {
// Test that profiling of division operations is okay, especially on ARM. See issue 6681.
func TestMathBigDivide(t *testing.T) {
testCPUProfile(t, nil, nil, nil, func(duration time.Duration) {
testCPUProfile(t, nil, func(duration time.Duration) {
t := time.After(duration)
pi := new(big.Int)
for {
@ -733,7 +758,8 @@ func stackContainsAll(spec string, count uintptr, stk []*profile.Location, label
}
func TestMorestack(t *testing.T) {
testCPUProfile(t, stackContainsAll, []string{"runtime.newstack,runtime/pprof.growstack"}, avoidFunctions(), func(duration time.Duration) {
matches := matchAndAvoidStacks(stackContainsAll, []string{"runtime.newstack,runtime/pprof.growstack"}, avoidFunctions())
testCPUProfile(t, matches, func(duration time.Duration) {
t := time.After(duration)
c := make(chan bool)
for {
@ -1364,7 +1390,8 @@ func stackContainsLabeled(spec string, count uintptr, stk []*profile.Location, l
}
func TestCPUProfileLabel(t *testing.T) {
testCPUProfile(t, stackContainsLabeled, []string{"runtime/pprof.cpuHogger;key=value"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContainsLabeled, []string{"runtime/pprof.cpuHogger;key=value"}, avoidFunctions())
testCPUProfile(t, matches, func(dur time.Duration) {
Do(context.Background(), Labels("key", "value"), func(context.Context) {
cpuHogger(cpuHog1, &salt1, dur)
})
@ -1375,7 +1402,8 @@ func TestLabelRace(t *testing.T) {
// Test the race detector annotations for synchronization
// between settings labels and consuming them from the
// profile.
testCPUProfile(t, stackContainsLabeled, []string{"runtime/pprof.cpuHogger;key=value"}, nil, func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContainsLabeled, []string{"runtime/pprof.cpuHogger;key=value"}, nil)
testCPUProfile(t, matches, func(dur time.Duration) {
start := time.Now()
var wg sync.WaitGroup
for time.Since(start) < dur {
@ -1394,6 +1422,86 @@ 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) {
Do(context.Background(), Labels("key", "value"), func(context.Context) {
var wg sync.WaitGroup
stop := make(chan struct{})
for i := 0; i < runtime.GOMAXPROCS(0); i++ {
wg.Add(1)
go func() {
defer wg.Done()
labelHog(stop)
}()
}
time.Sleep(dur)
close(stop)
wg.Wait()
})
})
}
// labelHog is designed to burn CPU time in a way that a high number of CPU
// samples end up running on systemstack.
func labelHog(stop chan struct{}) {
for i := 0; ; i++ {
select {
case <-stop:
return
default:
fmt.Fprintf(io.Discard, "%d", i)
}
}
}
// Check that there is no deadlock when the program receives SIGPROF while in
// 64bit atomics' critical section. Used to happen on mips{,le}. See #20146.
func TestAtomicLoadStore64(t *testing.T) {
@ -1686,7 +1794,8 @@ func TestTimeVDSO(t *testing.T) {
testenv.SkipFlaky(t, 48655)
}
p := testCPUProfile(t, stackContains, []string{"time.now"}, avoidFunctions(), func(dur time.Duration) {
matches := matchAndAvoidStacks(stackContains, []string{"time.now"}, avoidFunctions())
p := testCPUProfile(t, matches, func(dur time.Duration) {
t0 := time.Now()
for {
t := time.Now()

9
src/runtime/proc.go
View File

@ -4726,7 +4726,14 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
}
if prof.hz != 0 {
cpuprof.add(gp, stk[:n])
// Note: it can happen on Windows that we interrupted a system thread
// with no g, so gp could nil. The other nil checks are done out of
// caution, but not expected to be nil in practice.
var tagPtr *unsafe.Pointer
if gp != nil && gp.m != nil && gp.m.curg != nil {
tagPtr = &gp.m.curg.labels
}
cpuprof.add(tagPtr, stk[:n])
}
getg().m.mallocing--
}