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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 (
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) {
// 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) {
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.
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.
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/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/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 runtime values.
// Run a few GC cycles to get some of the stats to be non-zero.
// Read all the supported metrics through the metrics package.
descs, samples := prepareAllMetricsSamples()
// 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
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)
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 "/memory/classes/total:bytes": = samples[i].Value.Uint64()
case "/memory/classes/heap/objects:bytes":
objects.totalBytes = samples[i].Value.Uint64()
case "/gc/heap/objects:objects": = 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": = 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 "/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")
if != totalVirtual.want {
t.Errorf(`"/memory/classes/total:bytes" does not match sum of /memory/classes/**: got %d, want %d`,, totalVirtual.want)
if got, want := objects.allocs-objects.frees,; 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(, len(; 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( {
t.Error("allocs-by-size and frees-by-size buckets don't match in length")
} else if len(objects.alloc.Counts) != len( {
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 :=[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 :=
for i := range objects.alloc.Counts {
if objects.alloc.Counts[i] <[i] {
t.Errorf("found more allocs than frees in object dist bucket %d", i)
gotAlloc += objects.alloc.Counts[i]
gotFree +=[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)
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.
for i := 0; i < b.N; i++ {
start := time.Now()
latencies = append(latencies, time.Now().Sub(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.
// 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 {
samples[0][total].Name = descs[i].Name
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
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:
sum := func(us []uint64) uint64 {
total := uint64(0)
for _, u := range us {
total += u
return total
// Populate the first generation.
// Check to make sure that these metrics only grow monotonically.
for gen := 1; gen < 10; gen++ {
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)