Revert "runtime: improve runtime-internal mutex profile tests"

This reverts commit f9ba2cf (CL 586237)

Reason for revert: This is part of a patch series that changed the
handling of contended lock2/unlock2 calls, reducing the maximum
throughput of contended runtime.mutex values, and causing a performance
regression on applications where that is (or became) the bottleneck.

This test verifies that the semantics of the mutex profile for
runtime.mutex values matches that of sync.Mutex values. Without the rest
of the patch series, this test would correctly identify that Go 1.22's
semantics are incorrect (issue #66999).

Updates #66999
Updates #67585

Change-Id: Id06ae01d7bc91c94054c80d273e6530cb2d59d10
Reviewed-on: https://go-review.googlesource.com/c/go/+/589096
Reviewed-by: Michael Pratt <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Auto-Submit: Rhys Hiltner <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: rhysh

src/runtime/export_test.go

@@ -39,8 +39,6 @@ var Atoi32 = atoi32
 var ParseByteCount = parseByteCount
 
 var Nanotime = nanotime
-var Cputicks = cputicks
-var CyclesPerSecond = pprof_cyclesPerSecond
 var NetpollBreak = netpollBreak
 var Usleep = usleep
 

src/runtime/metrics_test.go

@@ -1008,9 +1008,9 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 		return metricGrowth, profileGrowth, p
 	}
 
-	testcase := func(strictTiming bool, acceptStacks [][]string, workers int, fn func() bool) func(t *testing.T) (metricGrowth float64, profileGrowth []int64, n, value int64) {
-		return func(t *testing.T) (metricGrowth float64, profileGrowth []int64, n, value int64) {
-			metricGrowth, totalProfileGrowth, p := measureDelta(t, func() {
+	testcase := func(strictTiming bool, acceptStacks [][]string, workers int, fn func() bool) func(t *testing.T) (metricGrowth, profileGrowth float64, n, value int64) {
+		return func(t *testing.T) (metricGrowth, profileGrowth float64, n, value int64) {
+			metricGrowth, profileGrowth, p := measureDelta(t, func() {
 				var started, stopped sync.WaitGroup
 				started.Add(workers)
 				stopped.Add(workers)
@@ -1030,7 +1030,7 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 				stopped.Wait()
 			})
 
-			if totalProfileGrowth == 0 {
+			if profileGrowth == 0 {
 				t.Errorf("no increase in mutex profile")
 			}
 			if metricGrowth == 0 && strictTiming {
@@ -1050,7 +1050,7 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 			// together. It doesn't work as well for user-space contention, where the
 			// involved goroutines are not _Grunnable the whole time and so need to pass
 			// through the scheduler.
-			t.Logf("lock contention growth in runtime/pprof's view  (%fs)", totalProfileGrowth)
+			t.Logf("lock contention growth in runtime/pprof's view  (%fs)", profileGrowth)
 			t.Logf("lock contention growth in runtime/metrics' view (%fs)", metricGrowth)
 
 			acceptStacks = append([][]string(nil), acceptStacks...)
@@ -1070,7 +1070,7 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 			}
 
 			var stks [][]string
-			values := make([][2]int64, len(acceptStacks)+1)
+			values := make([][2]int64, len(acceptStacks))
 			for _, s := range p.Sample {
 				var have []string
 				for _, loc := range s.Location {
@@ -1079,26 +1079,16 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 					}
 				}
 				stks = append(stks, have)
-				found := false
 				for i, stk := range acceptStacks {
 					if slices.Equal(have, stk) {
 						values[i][0] += s.Value[0]
 						values[i][1] += s.Value[1]
-						found = true
-						break
 					}
 				}
-				if !found {
-					values[len(values)-1][0] += s.Value[0]
-					values[len(values)-1][1] += s.Value[1]
-				}
 			}
-			profileGrowth = make([]int64, len(acceptStacks)+1)
-			profileGrowth[len(profileGrowth)-1] = values[len(values)-1][1]
 			for i, stk := range acceptStacks {
 				n += values[i][0]
 				value += values[i][1]
-				profileGrowth[i] = values[i][1]
 				t.Logf("stack %v has samples totaling n=%d value=%d", stk, values[i][0], values[i][1])
 			}
 			if n == 0 && value == 0 {
@@ -1120,14 +1110,8 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 	t.Run("runtime.lock", func(t *testing.T) {
 		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()
-		slowDelayMicros := baseDelay.Microseconds() * 4
-
-		const (
-			fastRole = 0
-			slowRole = 1
-		)
+		delay := 100 * time.Microsecond // large relative to system noise, for comparison between clocks
+		delayMicros := delay.Microseconds()
 
 		// The goroutine that acquires the lock will only proceed when it
 		// detects that its partner is contended for the lock. That will lead to
@@ -1143,69 +1127,34 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 			t.Skipf("contention on runtime-internal locks requires GOMAXPROCS >= %d", workers)
 		}
 
-		minTicks := make([][]int64, workers) // lower bound, known-contended time, measured by cputicks
-		maxTicks := make([][]int64, workers) // upper bound, total lock() duration, measured by cputicks
-		for i := range minTicks {
-			minTicks[i] = make([]int64, len(mus))
-			maxTicks[i] = make([]int64, len(mus))
-		}
-		var id atomic.Int32
 		fn := func() bool {
 			n := int(needContention.Load())
 			if n < 0 {
 				return false
 			}
 			mu := &mus[n]
 
-			// Each worker has a role: to have a fast or slow critical section.
-			// Rotate the role assignments as we step through the mutex slice so
-			// we don't end up with one M always claiming the same kind of work.
-			id := int(id.Add(1))
-			role := (id + n) % workers
-
-			marker, delayMicros := fastMarkerFrame, fastDelayMicros
-			if role == slowRole {
-				marker, delayMicros = slowMarkerFrame, slowDelayMicros
-			}
-
-			marker(func() {
-				t0 := runtime.Cputicks()
-				runtime.Lock(mu)
-				maxTicks[role][n] = runtime.Cputicks() - t0
-				minTicks[role][n] = 0
-				for int(needContention.Load()) == n {
-					if runtime.MutexContended(mu) {
-						t1 := runtime.Cputicks()
-						// make them wait a little while
-						for start := runtime.Nanotime(); (runtime.Nanotime()-start)/1000 < delayMicros; {
-							runtime.Usleep(uint32(1 + delayMicros/8))
-						}
-						minTicks[role][n] = runtime.Cputicks() - t1
-						break
+			runtime.Lock(mu)
+			for int(needContention.Load()) == n {
+				if runtime.MutexContended(mu) {
+					// make them wait a little while
+					for start := runtime.Nanotime(); (runtime.Nanotime()-start)/1000 < delayMicros; {
+						runtime.Usleep(uint32(delayMicros))
 					}
+					break
 				}
-				runtime.Unlock(mu)
-				needContention.Store(int64(n - 1))
-			})
+			}
+			runtime.Unlock(mu)
+			needContention.Store(int64(n - 1))
 
 			return true
 		}
 
-		stks := make([][]string, 2)
-		for i := range stks {
-			marker := "runtime_test.fastMarkerFrame"
-			if i == slowRole {
-				marker = "runtime_test.slowMarkerFrame"
-			}
-
-			stks[i] = []string{
-				"runtime.unlock",
-				"runtime_test." + name + ".func4.1.1",
-				marker,
-				"runtime_test." + name + ".func4.1",
-				"runtime_test.(*contentionWorker).run",
-			}
-		}
+		stks := [][]string{{
+			"runtime.unlock",
+			"runtime_test." + name + ".func4.1",
+			"runtime_test.(*contentionWorker).run",
+		}}
 
 		t.Run("sample-1", func(t *testing.T) {
 			old := runtime.SetMutexProfileFraction(1)
@@ -1215,11 +1164,11 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 			metricGrowth, profileGrowth, n, _ := testcase(true, stks, workers, fn)(t)
 
 			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.
+				// The runtime/metrics view may be 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 {
+				if have, want := metricGrowth, delay.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
@@ -1231,68 +1180,10 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 				t.Errorf("mutex profile reported contention count different from the known true count (%d != %d)", have, want)
 			}
 
-			var slowMinTicks, fastMinTicks int64
-			for role, ticks := range minTicks {
-				for _, delta := range ticks {
-					if role == slowRole {
-						slowMinTicks += delta
-					} else {
-						fastMinTicks += delta
-					}
-				}
-			}
-			var slowMaxTicks, fastMaxTicks int64
-			for role, ticks := range maxTicks {
-				for _, delta := range ticks {
-					if role == slowRole {
-						slowMaxTicks += delta
-					} else {
-						fastMaxTicks += delta
-					}
-				}
-			}
-
-			cpuGHz := float64(runtime.CyclesPerSecond()) / 1e9
-			for _, set := range []struct {
-				name     string
-				profTime int64
-				minTime  int64
-				maxTime  int64
-			}{
-				{
-					name:     "slow",
-					profTime: profileGrowth[slowRole],
-					minTime:  int64(float64(slowMinTicks) / cpuGHz),
-					maxTime:  int64(float64(fastMaxTicks) / cpuGHz),
-				},
-				{
-					name:     "fast",
-					profTime: profileGrowth[fastRole],
-					minTime:  int64(float64(fastMinTicks) / cpuGHz),
-					maxTime:  int64(float64(slowMaxTicks) / cpuGHz),
-				},
-			} {
-				t.Logf("profile's view of delays due to %q critical section:                 %dns", set.name, set.profTime)
-				t.Logf("test's view of known-contended time within %q critical section:      %dns", set.name, set.minTime)
-				t.Logf("test's view of lock duration before critical sections other than %q: %dns", set.name, set.maxTime)
-
-				if set.profTime < set.minTime {
-					t.Errorf("profile undercounted %q critical section", set.name)
-				}
-				if set.profTime > set.maxTime {
-					t.Errorf("profile overcounted %q critical section", set.name)
-				}
-			}
-
-			var totalProfileGrowth float64
-			for _, growth := range profileGrowth {
-				totalProfileGrowth += float64(growth) * time.Nanosecond.Seconds()
-			}
-
 			const slop = 1.5 // account for nanotime vs cputicks
 			t.Run("compare timers", func(t *testing.T) {
 				testenv.SkipFlaky(t, 64253)
-				if totalProfileGrowth > slop*metricGrowth || metricGrowth > slop*totalProfileGrowth {
+				if profileGrowth > slop*metricGrowth || metricGrowth > slop*profileGrowth {
 					t.Errorf("views differ by more than %fx", slop)
 				}
 			})
@@ -1313,7 +1204,7 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 			// 1e-9 chance of that, which is an acceptably low flakiness rate.
 			const samplingSlop = 2.5
 
-			if have, want := metricGrowth, baseDelay.Seconds()*float64(len(mus)); samplingSlop*have < want {
+			if have, want := metricGrowth, delay.Seconds()*float64(len(mus)); samplingSlop*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
@@ -1324,13 +1215,8 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 				t.Errorf("mutex profile reported contention count too different from the expected count (%d far from %d)", have, want)
 			}
 
-			var totalProfileGrowth float64
-			for _, growth := range profileGrowth {
-				totalProfileGrowth += float64(growth) * time.Nanosecond.Seconds()
-			}
-
 			const timerSlop = 1.5 * samplingSlop // account for nanotime vs cputicks, plus the two views' independent sampling
-			if totalProfileGrowth > timerSlop*metricGrowth || metricGrowth > timerSlop*totalProfileGrowth {
+			if profileGrowth > timerSlop*metricGrowth || metricGrowth > timerSlop*profileGrowth {
 				t.Errorf("views differ by more than %fx", timerSlop)
 			}
 		})
@@ -1397,9 +1283,6 @@ func TestRuntimeLockMetricsAndProfile(t *testing.T) {
 	})
 }
 
-func slowMarkerFrame(fn func()) { fn() }
-func fastMarkerFrame(fn func()) { fn() }
-
 // contentionWorker provides cleaner call stacks for lock contention profile tests
 type contentionWorker struct {
 	before func()