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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime_test
import (
"reflect"
"runtime"
"runtime/debug"
"runtime/metrics"
"sort"
"strings"
"sync"
"testing"
"time"
"unsafe"
)
func prepareAllMetricsSamples() (map[string]metrics.Description, []metrics.Sample) {
all := metrics.All()
samples := make([]metrics.Sample, len(all))
descs := make(map[string]metrics.Description)
for i := range all {
samples[i].Name = all[i].Name
descs[all[i].Name] = all[i]
}
return descs, samples
}
func TestReadMetrics(t *testing.T) {
// Run a GC cycle to get some of the stats to be non-zero.
runtime.GC()
// Set an arbitrary memory limit to check the metric for it
limit := int64(512 * 1024 * 1024)
oldLimit := debug.SetMemoryLimit(limit)
defer debug.SetMemoryLimit(oldLimit)
// Set an GC percent to check the metric for it
gcPercent := 99
oldGCPercent := debug.SetGCPercent(gcPercent)
defer debug.SetGCPercent(oldGCPercent)
// Tests whether readMetrics produces values aligning
// with ReadMemStats while the world is stopped.
var mstats runtime.MemStats
_, samples := prepareAllMetricsSamples()
runtime.ReadMetricsSlow(&mstats, unsafe.Pointer(&samples[0]), len(samples), cap(samples))
checkUint64 := func(t *testing.T, m string, got, want uint64) {
t.Helper()
if got != want {
t.Errorf("metric %q: got %d, want %d", m, got, want)
}
}
// Check to make sure the values we read line up with other values we read.
var allocsBySize *metrics.Float64Histogram
var tinyAllocs uint64
var mallocs, frees uint64
for i := range samples {
switch name := samples[i].Name; name {
case "/cgo/go-to-c-calls:calls":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(runtime.NumCgoCall()))
case "/memory/classes/heap/free:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapIdle-mstats.HeapReleased)
case "/memory/classes/heap/released:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapReleased)
case "/memory/classes/heap/objects:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapAlloc)
case "/memory/classes/heap/unused:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapInuse-mstats.HeapAlloc)
case "/memory/classes/heap/stacks:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.StackInuse)
case "/memory/classes/metadata/mcache/free:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.MCacheSys-mstats.MCacheInuse)
case "/memory/classes/metadata/mcache/inuse:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.MCacheInuse)
case "/memory/classes/metadata/mspan/free:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.MSpanSys-mstats.MSpanInuse)
case "/memory/classes/metadata/mspan/inuse:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.MSpanInuse)
case "/memory/classes/metadata/other:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.GCSys)
case "/memory/classes/os-stacks:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.StackSys-mstats.StackInuse)
case "/memory/classes/other:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.OtherSys)
case "/memory/classes/profiling/buckets:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.BuckHashSys)
case "/memory/classes/total:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.Sys)
case "/gc/heap/allocs-by-size:bytes":
hist := samples[i].Value.Float64Histogram()
// Skip size class 0 in BySize, because it's always empty and not represented
// in the histogram.
for i, sc := range mstats.BySize[1:] {
if b, s := hist.Buckets[i+1], float64(sc.Size+1); b != s {
t.Errorf("bucket does not match size class: got %f, want %f", b, s)
// The rest of the checks aren't expected to work anyway.
continue
}
if c, m := hist.Counts[i], sc.Mallocs; c != m {
t.Errorf("histogram counts do not much BySize for class %d: got %d, want %d", i, c, m)
}
}
allocsBySize = hist
case "/gc/heap/allocs:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.TotalAlloc)
case "/gc/heap/frees-by-size:bytes":
hist := samples[i].Value.Float64Histogram()
// Skip size class 0 in BySize, because it's always empty and not represented
// in the histogram.
for i, sc := range mstats.BySize[1:] {
if b, s := hist.Buckets[i+1], float64(sc.Size+1); b != s {
t.Errorf("bucket does not match size class: got %f, want %f", b, s)
// The rest of the checks aren't expected to work anyway.
continue
}
if c, f := hist.Counts[i], sc.Frees; c != f {
t.Errorf("histogram counts do not match BySize for class %d: got %d, want %d", i, c, f)
}
}
case "/gc/heap/frees:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.TotalAlloc-mstats.HeapAlloc)
case "/gc/heap/tiny/allocs:objects":
// Currently, MemStats adds tiny alloc count to both Mallocs AND Frees.
// The reason for this is because MemStats couldn't be extended at the time
// but there was a desire to have Mallocs at least be a little more representative,
// while having Mallocs - Frees still represent a live object count.
// Unfortunately, MemStats doesn't actually export a large allocation count,
// so it's impossible to pull this number out directly.
//
// Check tiny allocation count outside of this loop, by using the allocs-by-size
// histogram in order to figure out how many large objects there are.
tinyAllocs = samples[i].Value.Uint64()
// Because the next two metrics tests are checking against Mallocs and Frees,
// we can't check them directly for the same reason: we need to account for tiny
// allocations included in Mallocs and Frees.
case "/gc/heap/allocs:objects":
mallocs = samples[i].Value.Uint64()
case "/gc/heap/frees:objects":
frees = samples[i].Value.Uint64()
case "/gc/heap/live:bytes":
// Check for "obviously wrong" values. We can't check a stronger invariant,
// such as live <= HeapAlloc, because live is not 100% accurate. It's computed
// under racy conditions, and some objects may be double-counted (this is
// intentional and necessary for GC performance).
//
// Instead, check against a much more reasonable upper-bound: the amount of
// mapped heap memory. We can't possibly overcount to the point of exceeding
// total mapped heap memory, except if there's an accounting bug.
if live := samples[i].Value.Uint64(); live > mstats.HeapSys {
t.Errorf("live bytes: %d > heap sys: %d", live, mstats.HeapSys)
} else if live == 0 {
// Might happen if we don't call runtime.GC() above.
t.Error("live bytes is 0")
}
case "/gc/gomemlimit:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(limit))
case "/gc/heap/objects:objects":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapObjects)
case "/gc/heap/goal:bytes":
checkUint64(t, name, samples[i].Value.Uint64(), mstats.NextGC)
case "/gc/gogc:percent":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(gcPercent))
case "/gc/cycles/automatic:gc-cycles":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumGC-mstats.NumForcedGC))
case "/gc/cycles/forced:gc-cycles":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumForcedGC))
case "/gc/cycles/total:gc-cycles":
checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumGC))
}
}
// Check tinyAllocs.
nonTinyAllocs := uint64(0)
for _, c := range allocsBySize.Counts {
nonTinyAllocs += c
}
checkUint64(t, "/gc/heap/tiny/allocs:objects", tinyAllocs, mstats.Mallocs-nonTinyAllocs)
// Check allocation and free counts.
checkUint64(t, "/gc/heap/allocs:objects", mallocs, mstats.Mallocs-tinyAllocs)
checkUint64(t, "/gc/heap/frees:objects", frees, mstats.Frees-tinyAllocs)
}
func TestReadMetricsConsistency(t *testing.T) {
// Tests whether readMetrics produces consistent, sensible values.
// The values are read concurrently with the runtime doing other
// things (e.g. allocating) so what we read can't reasonably compared
// to other runtime values (e.g. MemStats).
// Run a few GC cycles to get some of the stats to be non-zero.
runtime.GC()
runtime.GC()
runtime.GC()
// Set GOMAXPROCS high then sleep briefly to ensure we generate
// some idle time.
oldmaxprocs := runtime.GOMAXPROCS(10)
time.Sleep(time.Millisecond)
runtime.GOMAXPROCS(oldmaxprocs)
// Read all the supported metrics through the metrics package.
descs, samples := prepareAllMetricsSamples()
metrics.Read(samples)
// Check to make sure the values we read make sense.
var totalVirtual struct {
got, want uint64
}
var objects struct {
alloc, free *metrics.Float64Histogram
allocs, frees uint64
allocdBytes, freedBytes uint64
total, totalBytes uint64
}
var gc struct {
numGC uint64
pauses uint64
}
var totalScan struct {
got, want uint64
}
var cpu struct {
gcAssist float64
gcDedicated float64
gcIdle float64
gcPause float64
gcTotal float64
idle float64
user float64
scavengeAssist float64
scavengeBg float64
scavengeTotal float64
total float64
}
for i := range samples {
kind := samples[i].Value.Kind()
if want := descs[samples[i].Name].Kind; kind != want {
t.Errorf("supported metric %q has unexpected kind: got %d, want %d", samples[i].Name, kind, want)
continue
}
if samples[i].Name != "/memory/classes/total:bytes" && strings.HasPrefix(samples[i].Name, "/memory/classes") {
v := samples[i].Value.Uint64()
totalVirtual.want += v
// None of these stats should ever get this big.
// If they do, there's probably overflow involved,
// usually due to bad accounting.
if int64(v) < 0 {
t.Errorf("%q has high/negative value: %d", samples[i].Name, v)
}
}
switch samples[i].Name {
case "/cpu/classes/gc/mark/assist:cpu-seconds":
cpu.gcAssist = samples[i].Value.Float64()
case "/cpu/classes/gc/mark/dedicated:cpu-seconds":
cpu.gcDedicated = samples[i].Value.Float64()
case "/cpu/classes/gc/mark/idle:cpu-seconds":
cpu.gcIdle = samples[i].Value.Float64()
case "/cpu/classes/gc/pause:cpu-seconds":
cpu.gcPause = samples[i].Value.Float64()
case "/cpu/classes/gc/total:cpu-seconds":
cpu.gcTotal = samples[i].Value.Float64()
case "/cpu/classes/idle:cpu-seconds":
cpu.idle = samples[i].Value.Float64()
case "/cpu/classes/scavenge/assist:cpu-seconds":
cpu.scavengeAssist = samples[i].Value.Float64()
case "/cpu/classes/scavenge/background:cpu-seconds":
cpu.scavengeBg = samples[i].Value.Float64()
case "/cpu/classes/scavenge/total:cpu-seconds":
cpu.scavengeTotal = samples[i].Value.Float64()
case "/cpu/classes/total:cpu-seconds":
cpu.total = samples[i].Value.Float64()
case "/cpu/classes/user:cpu-seconds":
cpu.user = samples[i].Value.Float64()
case "/memory/classes/total:bytes":
totalVirtual.got = samples[i].Value.Uint64()
case "/memory/classes/heap/objects:bytes":
objects.totalBytes = samples[i].Value.Uint64()
case "/gc/heap/objects:objects":
objects.total = samples[i].Value.Uint64()
case "/gc/heap/allocs:bytes":
objects.allocdBytes = samples[i].Value.Uint64()
case "/gc/heap/allocs:objects":
objects.allocs = samples[i].Value.Uint64()
case "/gc/heap/allocs-by-size:bytes":
objects.alloc = samples[i].Value.Float64Histogram()
case "/gc/heap/frees:bytes":
objects.freedBytes = samples[i].Value.Uint64()
case "/gc/heap/frees:objects":
objects.frees = samples[i].Value.Uint64()
case "/gc/heap/frees-by-size:bytes":
objects.free = samples[i].Value.Float64Histogram()
case "/gc/cycles:gc-cycles":
gc.numGC = samples[i].Value.Uint64()
case "/gc/pauses:seconds":
h := samples[i].Value.Float64Histogram()
gc.pauses = 0
for i := range h.Counts {
gc.pauses += h.Counts[i]
}
case "/gc/scan/heap:bytes":
totalScan.want += samples[i].Value.Uint64()
case "/gc/scan/globals:bytes":
totalScan.want += samples[i].Value.Uint64()
case "/gc/scan/stack:bytes":
totalScan.want += samples[i].Value.Uint64()
case "/gc/scan/total:bytes":
totalScan.got = samples[i].Value.Uint64()
case "/sched/gomaxprocs:threads":
if got, want := samples[i].Value.Uint64(), uint64(runtime.GOMAXPROCS(-1)); got != want {
t.Errorf("gomaxprocs doesn't match runtime.GOMAXPROCS: got %d, want %d", got, want)
}
case "/sched/goroutines:goroutines":
if samples[i].Value.Uint64() < 1 {
t.Error("number of goroutines is less than one")
}
}
}
// Only check this on Linux where we can be reasonably sure we have a high-resolution timer.
if runtime.GOOS == "linux" {
if cpu.gcDedicated <= 0 && cpu.gcAssist <= 0 && cpu.gcIdle <= 0 {
t.Errorf("found no time spent on GC work: %#v", cpu)
}
if cpu.gcPause <= 0 {
t.Errorf("found no GC pauses: %f", cpu.gcPause)
}
if cpu.idle <= 0 {
t.Errorf("found no idle time: %f", cpu.idle)
}
if total := cpu.gcDedicated + cpu.gcAssist + cpu.gcIdle + cpu.gcPause; !withinEpsilon(cpu.gcTotal, total, 0.01) {
t.Errorf("calculated total GC CPU not within 1%% of sampled total: %f vs. %f", total, cpu.gcTotal)
}
if total := cpu.scavengeAssist + cpu.scavengeBg; !withinEpsilon(cpu.scavengeTotal, total, 0.01) {
t.Errorf("calculated total scavenge CPU not within 1%% of sampled total: %f vs. %f", total, cpu.scavengeTotal)
}
if cpu.total <= 0 {
t.Errorf("found no total CPU time passed")
}
if cpu.user <= 0 {
t.Errorf("found no user time passed")
}
if total := cpu.gcTotal + cpu.scavengeTotal + cpu.user + cpu.idle; !withinEpsilon(cpu.total, total, 0.02) {
t.Errorf("calculated total CPU not within 2%% of sampled total: %f vs. %f", total, cpu.total)
}
}
if totalVirtual.got != totalVirtual.want {
t.Errorf(`"/memory/classes/total:bytes" does not match sum of /memory/classes/**: got %d, want %d`, totalVirtual.got, totalVirtual.want)
}
if got, want := objects.allocs-objects.frees, objects.total; got != want {
t.Errorf("mismatch between object alloc/free tallies and total: got %d, want %d", got, want)
}
if got, want := objects.allocdBytes-objects.freedBytes, objects.totalBytes; got != want {
t.Errorf("mismatch between object alloc/free tallies and total: got %d, want %d", got, want)
}
if b, c := len(objects.alloc.Buckets), len(objects.alloc.Counts); b != c+1 {
t.Errorf("allocs-by-size has wrong bucket or counts length: %d buckets, %d counts", b, c)
}
if b, c := len(objects.free.Buckets), len(objects.free.Counts); b != c+1 {
t.Errorf("frees-by-size has wrong bucket or counts length: %d buckets, %d counts", b, c)
}
if len(objects.alloc.Buckets) != len(objects.free.Buckets) {
t.Error("allocs-by-size and frees-by-size buckets don't match in length")
} else if len(objects.alloc.Counts) != len(objects.free.Counts) {
t.Error("allocs-by-size and frees-by-size counts don't match in length")
} else {
for i := range objects.alloc.Buckets {
ba := objects.alloc.Buckets[i]
bf := objects.free.Buckets[i]
if ba != bf {
t.Errorf("bucket %d is different for alloc and free hists: %f != %f", i, ba, bf)
}
}
if !t.Failed() {
var gotAlloc, gotFree uint64
want := objects.total
for i := range objects.alloc.Counts {
if objects.alloc.Counts[i] < objects.free.Counts[i] {
t.Errorf("found more allocs than frees in object dist bucket %d", i)
continue
}
gotAlloc += objects.alloc.Counts[i]
gotFree += objects.free.Counts[i]
}
if got := gotAlloc - gotFree; got != want {
t.Errorf("object distribution counts don't match count of live objects: got %d, want %d", got, want)
}
if gotAlloc != objects.allocs {
t.Errorf("object distribution counts don't match total allocs: got %d, want %d", gotAlloc, objects.allocs)
}
if gotFree != objects.frees {
t.Errorf("object distribution counts don't match total allocs: got %d, want %d", gotFree, objects.frees)
}
}
}
// The current GC has at least 2 pauses per GC.
// Check to see if that value makes sense.
if gc.pauses < gc.numGC*2 {
t.Errorf("fewer pauses than expected: got %d, want at least %d", gc.pauses, gc.numGC*2)
}
if totalScan.got <= 0 {
t.Errorf("scannable GC space is empty: %d", totalScan.got)
}
if totalScan.got != totalScan.want {
t.Errorf("/gc/scan/total:bytes doesn't line up with sum of /gc/scan*: total %d vs. sum %d", totalScan.got, totalScan.want)
}
}
func BenchmarkReadMetricsLatency(b *testing.B) {
stop := applyGCLoad(b)
// Spend this much time measuring latencies.
latencies := make([]time.Duration, 0, 1024)
_, samples := prepareAllMetricsSamples()
// Hit metrics.Read continuously and measure.
b.ResetTimer()
for i := 0; i < b.N; i++ {
start := time.Now()
metrics.Read(samples)
latencies = append(latencies, time.Since(start))
}
// Make sure to stop the timer before we wait! The load created above
// is very heavy-weight and not easy to stop, so we could end up
// confusing the benchmarking framework for small b.N.
b.StopTimer()
stop()
// Disable the default */op metrics.
// ns/op doesn't mean anything because it's an average, but we
// have a sleep in our b.N loop above which skews this significantly.
b.ReportMetric(0, "ns/op")
b.ReportMetric(0, "B/op")
b.ReportMetric(0, "allocs/op")
// Sort latencies then report percentiles.
sort.Slice(latencies, func(i, j int) bool {
return latencies[i] < latencies[j]
})
b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
}
var readMetricsSink [1024]interface{}
func TestReadMetricsCumulative(t *testing.T) {
// Set up the set of metrics marked cumulative.
descs := metrics.All()
var samples [2][]metrics.Sample
samples[0] = make([]metrics.Sample, len(descs))
samples[1] = make([]metrics.Sample, len(descs))
total := 0
for i := range samples[0] {
if !descs[i].Cumulative {
continue
}
samples[0][total].Name = descs[i].Name
total++
}
samples[0] = samples[0][:total]
samples[1] = samples[1][:total]
copy(samples[1], samples[0])
// Start some noise in the background.
var wg sync.WaitGroup
wg.Add(1)
done := make(chan struct{})
go func() {
defer wg.Done()
for {
// Add more things here that could influence metrics.
for i := 0; i < len(readMetricsSink); i++ {
readMetricsSink[i] = make([]byte, 1024)
select {
case <-done:
return
default:
}
}
runtime.GC()
}
}()
sum := func(us []uint64) uint64 {
total := uint64(0)
for _, u := range us {
total += u
}
return total
}
// Populate the first generation.
metrics.Read(samples[0])
// Check to make sure that these metrics only grow monotonically.
for gen := 1; gen < 10; gen++ {
metrics.Read(samples[gen%2])
for i := range samples[gen%2] {
name := samples[gen%2][i].Name
vNew, vOld := samples[gen%2][i].Value, samples[1-(gen%2)][i].Value
switch vNew.Kind() {
case metrics.KindUint64:
new := vNew.Uint64()
old := vOld.Uint64()
if new < old {
t.Errorf("%s decreased: %d < %d", name, new, old)
}
case metrics.KindFloat64:
new := vNew.Float64()
old := vOld.Float64()
if new < old {
t.Errorf("%s decreased: %f < %f", name, new, old)
}
case metrics.KindFloat64Histogram:
new := sum(vNew.Float64Histogram().Counts)
old := sum(vOld.Float64Histogram().Counts)
if new < old {
t.Errorf("%s counts decreased: %d < %d", name, new, old)
}
}
}
}
close(done)
wg.Wait()
}
func withinEpsilon(v1, v2, e float64) bool {
return v2-v2*e <= v1 && v1 <= v2+v2*e
}
func TestMutexWaitTimeMetric(t *testing.T) {
var sample [1]metrics.Sample
sample[0].Name = "/sync/mutex/wait/total:seconds"
locks := []locker2{
new(mutex),
new(rwmutexWrite),
new(rwmutexReadWrite),
new(rwmutexWriteRead),
}
for _, lock := range locks {
t.Run(reflect.TypeOf(lock).Elem().Name(), func(t *testing.T) {
metrics.Read(sample[:])
before := time.Duration(sample[0].Value.Float64() * 1e9)
minMutexWaitTime := generateMutexWaitTime(lock)
metrics.Read(sample[:])
after := time.Duration(sample[0].Value.Float64() * 1e9)
if wt := after - before; wt < minMutexWaitTime {
t.Errorf("too little mutex wait time: got %s, want %s", wt, minMutexWaitTime)
}
})
}
}
// locker2 represents an API surface of two concurrent goroutines
// locking the same resource, but through different APIs. It's intended
// to abstract over the relationship of two Lock calls or an RLock
// and a Lock call.
type locker2 interface {
Lock1()
Unlock1()
Lock2()
Unlock2()
}
type mutex struct {
mu sync.Mutex
}
func (m *mutex) Lock1() { m.mu.Lock() }
func (m *mutex) Unlock1() { m.mu.Unlock() }
func (m *mutex) Lock2() { m.mu.Lock() }
func (m *mutex) Unlock2() { m.mu.Unlock() }
type rwmutexWrite struct {
mu sync.RWMutex
}
func (m *rwmutexWrite) Lock1() { m.mu.Lock() }
func (m *rwmutexWrite) Unlock1() { m.mu.Unlock() }
func (m *rwmutexWrite) Lock2() { m.mu.Lock() }
func (m *rwmutexWrite) Unlock2() { m.mu.Unlock() }
type rwmutexReadWrite struct {
mu sync.RWMutex
}
func (m *rwmutexReadWrite) Lock1() { m.mu.RLock() }
func (m *rwmutexReadWrite) Unlock1() { m.mu.RUnlock() }
func (m *rwmutexReadWrite) Lock2() { m.mu.Lock() }
func (m *rwmutexReadWrite) Unlock2() { m.mu.Unlock() }
type rwmutexWriteRead struct {
mu sync.RWMutex
}
func (m *rwmutexWriteRead) Lock1() { m.mu.Lock() }
func (m *rwmutexWriteRead) Unlock1() { m.mu.Unlock() }
func (m *rwmutexWriteRead) Lock2() { m.mu.RLock() }
func (m *rwmutexWriteRead) Unlock2() { m.mu.RUnlock() }
// generateMutexWaitTime causes a couple of goroutines
// to block a whole bunch of times on a sync.Mutex, returning
// the minimum amount of time that should be visible in the
// /sync/mutex-wait:seconds metric.
func generateMutexWaitTime(mu locker2) time.Duration {
// Set up the runtime to always track casgstatus transitions for metrics.
*runtime.CasGStatusAlwaysTrack = true
mu.Lock1()
// Start up a goroutine to wait on the lock.
gc := make(chan *runtime.G)
done := make(chan bool)
go func() {
gc <- runtime.Getg()
for {
mu.Lock2()
mu.Unlock2()
if <-done {
return
}
}
}()
gp := <-gc
// Set the block time high enough so that it will always show up, even
// on systems with coarse timer granularity.
const blockTime = 100 * time.Millisecond
// Make sure the goroutine spawned above actually blocks on the lock.
for {
if runtime.GIsWaitingOnMutex(gp) {
break
}
runtime.Gosched()
}
// Let some amount of time pass.
time.Sleep(blockTime)
// Let the other goroutine acquire the lock.
mu.Unlock1()
done <- true
// Reset flag.
*runtime.CasGStatusAlwaysTrack = false
return blockTime
}
// See issue #60276.
func TestCPUMetricsSleep(t *testing.T) {
if runtime.GOOS == "wasip1" {
// Since wasip1 busy-waits in the scheduler, there's no meaningful idle
// time. This is accurately reflected in the metrics, but it means this
// test is basically meaningless on this platform.
t.Skip("wasip1 currently busy-waits in idle time; test not applicable")
}
names := []string{
"/cpu/classes/idle:cpu-seconds",
"/cpu/classes/gc/mark/assist:cpu-seconds",
"/cpu/classes/gc/mark/dedicated:cpu-seconds",
"/cpu/classes/gc/mark/idle:cpu-seconds",
"/cpu/classes/gc/pause:cpu-seconds",
"/cpu/classes/gc/total:cpu-seconds",
"/cpu/classes/scavenge/assist:cpu-seconds",
"/cpu/classes/scavenge/background:cpu-seconds",
"/cpu/classes/scavenge/total:cpu-seconds",
"/cpu/classes/total:cpu-seconds",
"/cpu/classes/user:cpu-seconds",
}
prep := func() []metrics.Sample {
mm := make([]metrics.Sample, len(names))
for i := range names {
mm[i].Name = names[i]
}
return mm
}
m1, m2 := prep(), prep()
const (
// Expected time spent idle.
dur = 100 * time.Millisecond
// maxFailures is the number of consecutive failures requires to cause the test to fail.
maxFailures = 10
)
failureIdleTimes := make([]float64, 0, maxFailures)
// If the bug we expect is happening, then the Sleep CPU time will be accounted for
// as user time rather than idle time. In an ideal world we'd expect the whole application
// to go instantly idle the moment this goroutine goes to sleep, and stay asleep for that
// duration. However, the Go runtime can easily eat into idle time while this goroutine is
// blocked in a sleep. For example, slow platforms might spend more time expected in the
// scheduler. Another example is that a Go runtime background goroutine could run while
// everything else is idle. Lastly, if a running goroutine is descheduled by the OS, enough
// time may pass such that the goroutine is ready to wake, even though the runtime couldn't
// observe itself as idle with nanotime.
//
// To deal with all this, we give a half-proc's worth of leniency.
//
// We also retry multiple times to deal with the fact that the OS might deschedule us before
// we yield and go idle. That has a rare enough chance that retries should resolve it.
// If the issue we expect is happening, it should be persistent.
minIdleCPUSeconds := dur.Seconds() * (float64(runtime.GOMAXPROCS(-1)) - 0.5)
// Let's make sure there's no background scavenge work to do.
//
// The runtime.GC calls below ensure the background sweeper
// will not run during the idle period.
debug.FreeOSMemory()
for retries := 0; retries < maxFailures; retries++ {
// Read 1.
runtime.GC() // Update /cpu/classes metrics.
metrics.Read(m1)
// Sleep.
time.Sleep(dur)
// Read 2.
runtime.GC() // Update /cpu/classes metrics.
metrics.Read(m2)
dt := m2[0].Value.Float64() - m1[0].Value.Float64()
if dt >= minIdleCPUSeconds {
// All is well. Test passed.
return
}
failureIdleTimes = append(failureIdleTimes, dt)
// Try again.
}
// We couldn't observe the expected idle time even once.
for i, dt := range failureIdleTimes {
t.Logf("try %2d: idle time = %.5fs\n", i+1, dt)
}
t.Logf("try %d breakdown:\n", len(failureIdleTimes))
for i := range names {
if m1[i].Value.Kind() == metrics.KindBad {
continue
}
t.Logf("\t%s %0.3f\n", names[i], m2[i].Value.Float64()-m1[i].Value.Float64())
}
t.Errorf(`time.Sleep did not contribute enough to "idle" class: minimum idle time = %.5fs`, minIdleCPUSeconds)
}