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runtime: lower mutex contention test expectations

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As of https://go.dev/cl/586796, the runtime/metrics view of internal
mutex contention is sampled at 1 per gTrackingPeriod, rather than either
1 (immediately prior to CL 586796) or the more frequent of
gTrackingPeriod or the mutex profiling rate (Go 1.22). Thus, we no
longer have a real lower bound on the amount of contention that
runtime/metrics will report. Relax the test's expectations again.

For #64253

Change-Id: I94e1d92348a03599a819ec8ac785a0eb3c1ddd73
Reviewed-on: https://go-review.googlesource.com/c/go/+/587515
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>
This commit is contained in:
Rhys Hiltner 2024-05-22 11:53:36 -07:00 • committed by Gopher Robot
parent b6fa505c4a
commit ac6dea7aa1
1 changed files with 21 additions and 8 deletions
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29
src/runtime/metrics_test.go
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@ -1036,6 +1036,13 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
if metricGrowth == 0 && strictTiming {
// If the critical section is very short, systems with low timer
// resolution may be unable to measure it via nanotime.
//
// This is sampled at 1 per gTrackingPeriod, but the explicit
// runtime.mutex tests create 200 contention events. Observing
// zero of those has a probability of (7/8)^200 = 2.5e-12 which
// is acceptably low (though the calculation has a tenuous
// dependency on cheaprandn being a good-enough source of
// entropy).
t.Errorf("no increase in /sync/mutex/wait/total:seconds metric")
}
// This comparison is possible because the time measurements in support of
@ -1111,7 +1118,7 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
name := t.Name()
t.Run("runtime.lock", func(t *testing.T) {
mus := make([]runtime.Mutex, 100)
mus := make([]runtime.Mutex, 200)
var needContention atomic.Int64
baseDelay := 100 * time.Microsecond // large relative to system noise, for comparison between clocks
fastDelayMicros := baseDelay.Microseconds()
@ -1207,13 +1214,19 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
needContention.Store(int64(len(mus) - 1))
metricGrowth, profileGrowth, n, _ := testcase(true, stks, workers, fn)(t)
if have, want := metricGrowth, baseDelay.Seconds()*float64(len(mus)); have < want {
// The test imposes a delay with usleep, verified with calls to
// nanotime. Compare against the runtime/metrics package's view
// (based on nanotime) rather than runtime/pprof's view (based
// on cputicks).
t.Errorf("runtime/metrics reported less than the known minimum contention duration (%fs < %fs)", have, want)
}
t.Run("metric", func(t *testing.T) {
// The runtime/metrics view is sampled at 1 per gTrackingPeriod,
// so we don't have a hard lower bound here.
testenv.SkipFlaky(t, 64253)
if have, want := metricGrowth, baseDelay.Seconds()*float64(len(mus)); have < want {
// The test imposes a delay with usleep, verified with calls to
// nanotime. Compare against the runtime/metrics package's view
// (based on nanotime) rather than runtime/pprof's view (based
// on cputicks).
t.Errorf("runtime/metrics reported less than the known minimum contention duration (%fs < %fs)", have, want)
}
})
if have, want := n, int64(len(mus)); have != want {
t.Errorf("mutex profile reported contention count different from the known true count (%d != %d)", have, want)
}