Preview: heapsampling.go
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/proc/thread-self/root/opt/golang/1.22.0/test/heapsampling.go
// run
// Copyright 2009 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.
// Test heap sampling logic.
package main
import (
"fmt"
"math"
"runtime"
)
var a16 *[16]byte
var a512 *[512]byte
var a256 *[256]byte
var a1k *[1024]byte
var a16k *[16 * 1024]byte
var a17k *[17 * 1024]byte
var a18k *[18 * 1024]byte
// This test checks that heap sampling produces reasonable results.
// Note that heap sampling uses randomization, so the results vary for
// run to run. To avoid flakes, this test performs multiple
// experiments and only complains if all of them consistently fail.
func main() {
// Sample at 16K instead of default 512K to exercise sampling more heavily.
runtime.MemProfileRate = 16 * 1024
if err := testInterleavedAllocations(); err != nil {
panic(err.Error())
}
if err := testSmallAllocations(); err != nil {
panic(err.Error())
}
}
// Repeatedly exercise a set of allocations and check that the heap
// profile collected by the runtime unsamples to a reasonable
// value. Because sampling is based on randomization, there can be
// significant variability on the unsampled data. To account for that,
// the testcase allows for a 10% margin of error, but only fails if it
// consistently fails across three experiments, avoiding flakes.
func testInterleavedAllocations() error {
const iters = 50000
// Sizes of the allocations performed by each experiment.
frames := []string{"main.allocInterleaved1", "main.allocInterleaved2", "main.allocInterleaved3"}
// Pass if at least one of three experiments has no errors. Use a separate
// function for each experiment to identify each experiment in the profile.
allocInterleaved1(iters)
if checkAllocations(getMemProfileRecords(), frames[0:1], iters, allocInterleavedSizes) == nil {
// Passed on first try, report no error.
return nil
}
allocInterleaved2(iters)
if checkAllocations(getMemProfileRecords(), frames[0:2], iters, allocInterleavedSizes) == nil {
// Passed on second try, report no error.
return nil
}
allocInterleaved3(iters)
// If it fails a third time, we may be onto something.
return checkAllocations(getMemProfileRecords(), frames[0:3], iters, allocInterleavedSizes)
}
var allocInterleavedSizes = []int64{17 * 1024, 1024, 18 * 1024, 512, 16 * 1024, 256}
// allocInterleaved stress-tests the heap sampling logic by interleaving large and small allocations.
func allocInterleaved(n int) {
for i := 0; i < n; i++ {
// Test verification depends on these lines being contiguous.
a17k = new([17 * 1024]byte)
a1k = new([1024]byte)
a18k = new([18 * 1024]byte)
a512 = new([512]byte)
a16k = new([16 * 1024]byte)
a256 = new([256]byte)
// Test verification depends on these lines being contiguous.
// Slow down the allocation rate to avoid #52433.
runtime.Gosched()
}
}
func allocInterleaved1(n int) {
allocInterleaved(n)
}
func allocInterleaved2(n int) {
allocInterleaved(n)
}
func allocInterleaved3(n int) {
allocInterleaved(n)
}
// Repeatedly exercise a set of allocations and check that the heap
// profile collected by the runtime unsamples to a reasonable
// value. Because sampling is based on randomization, there can be
// significant variability on the unsampled data. To account for that,
// the testcase allows for a 10% margin of error, but only fails if it
// consistently fails across three experiments, avoiding flakes.
func testSmallAllocations() error {
const iters = 50000
// Sizes of the allocations performed by each experiment.
sizes := []int64{1024, 512, 256}
frames := []string{"main.allocSmall1", "main.allocSmall2", "main.allocSmall3"}
// Pass if at least one of three experiments has no errors. Use a separate
// function for each experiment to identify each experiment in the profile.
allocSmall1(iters)
if checkAllocations(getMemProfileRecords(), frames[0:1], iters, sizes) == nil {
// Passed on first try, report no error.
return nil
}
allocSmall2(iters)
if checkAllocations(getMemProfileRecords(), frames[0:2], iters, sizes) == nil {
// Passed on second try, report no error.
return nil
}
allocSmall3(iters)
// If it fails a third time, we may be onto something.
return checkAllocations(getMemProfileRecords(), frames[0:3], iters, sizes)
}
// allocSmall performs only small allocations for sanity testing.
func allocSmall(n int) {
for i := 0; i < n; i++ {
// Test verification depends on these lines being contiguous.
a1k = new([1024]byte)
a512 = new([512]byte)
a256 = new([256]byte)
// Slow down the allocation rate to avoid #52433.
runtime.Gosched()
}
}
// Three separate instances of testing to avoid flakes. Will report an error
// only if they all consistently report failures.
func allocSmall1(n int) {
allocSmall(n)
}
func allocSmall2(n int) {
allocSmall(n)
}
func allocSmall3(n int) {
allocSmall(n)
}
// checkAllocations validates that the profile records collected for
// the named function are consistent with count contiguous allocations
// of the specified sizes.
// Check multiple functions and only report consistent failures across
// multiple tests.
// Look only at samples that include the named frames, and group the
// allocations by their line number. All these allocations are done from
// the same leaf function, so their line numbers are the same.
func checkAllocations(records []runtime.MemProfileRecord, frames []string, count int64, size []int64) error {
objectsPerLine := map[int][]int64{}
bytesPerLine := map[int][]int64{}
totalCount := []int64{}
// Compute the line number of the first allocation. All the
// allocations are from the same leaf, so pick the first one.
var firstLine int
for ln := range allocObjects(records, frames[0]) {
if firstLine == 0 || firstLine > ln {
firstLine = ln
}
}
for _, frame := range frames {
var objectCount int64
a := allocObjects(records, frame)
for s := range size {
// Allocations of size size[s] should be on line firstLine + s.
ln := firstLine + s
objectsPerLine[ln] = append(objectsPerLine[ln], a[ln].objects)
bytesPerLine[ln] = append(bytesPerLine[ln], a[ln].bytes)
objectCount += a[ln].objects
}
totalCount = append(totalCount, objectCount)
}
for i, w := range size {
ln := firstLine + i
if err := checkValue(frames[0], ln, "objects", count, objectsPerLine[ln]); err != nil {
return err
}
if err := checkValue(frames[0], ln, "bytes", count*w, bytesPerLine[ln]); err != nil {
return err
}
}
return checkValue(frames[0], 0, "total", count*int64(len(size)), totalCount)
}
// checkValue checks an unsampled value against its expected value.
// Given that this is a sampled value, it will be unexact and will change
// from run to run. Only report it as a failure if all the values land
// consistently far from the expected value.
func checkValue(fname string, ln int, testName string, want int64, got []int64) error {
if got == nil {
return fmt.Errorf("Unexpected empty result")
}
min, max := got[0], got[0]
for _, g := range got[1:] {
if g < min {
min = g
}
if g > max {
max = g
}
}
margin := want / 10 // 10% margin.
if min > want+margin || max < want-margin {
return fmt.Errorf("%s:%d want %s in [%d: %d], got %v", fname, ln, testName, want-margin, want+margin, got)
}
return nil
}
func getMemProfileRecords() []runtime.MemProfileRecord {
// Force the runtime to update the object and byte counts.
// This can take up to two GC cycles to get a complete
// snapshot of the current point in time.
runtime.GC()
runtime.GC()
// Find out how many records there are (MemProfile(nil, true)),
// allocate that many records, and get the data.
// There's a race—more records might be added between
// the two calls—so allocate a few extra records for safety
// and also try again if we're very unlucky.
// The loop should only execute one iteration in the common case.
var p []runtime.MemProfileRecord
n, ok := runtime.MemProfile(nil, true)
for {
// Allocate room for a slightly bigger profile,
// in case a few more entries have been added
// since the call to MemProfile.
p = make([]runtime.MemProfileRecord, n+50)
n, ok = runtime.MemProfile(p, true)
if ok {
p = p[0:n]
break
}
// Profile grew; try again.
}
return p
}
type allocStat struct {
bytes, objects int64
}
// allocObjects examines the profile records for samples including the
// named function and returns the allocation stats aggregated by
// source line number of the allocation (at the leaf frame).
func allocObjects(records []runtime.MemProfileRecord, function string) map[int]allocStat {
a := make(map[int]allocStat)
for _, r := range records {
var pcs []uintptr
for _, s := range r.Stack0 {
if s == 0 {
break
}
pcs = append(pcs, s)
}
frames := runtime.CallersFrames(pcs)
line := 0
for {
frame, more := frames.Next()
name := frame.Function
if line == 0 {
line = frame.Line
}
if name == function {
allocStat := a[line]
allocStat.bytes += r.AllocBytes
allocStat.objects += r.AllocObjects
a[line] = allocStat
}
if !more {
break
}
}
}
for line, stats := range a {
objects, bytes := scaleHeapSample(stats.objects, stats.bytes, int64(runtime.MemProfileRate))
a[line] = allocStat{bytes, objects}
}
return a
}
// scaleHeapSample unsamples heap allocations.
// Taken from src/cmd/pprof/internal/profile/legacy_profile.go
func scaleHeapSample(count, size, rate int64) (int64, int64) {
if count == 0 || size == 0 {
return 0, 0
}
if rate <= 1 {
// if rate==1 all samples were collected so no adjustment is needed.
// if rate<1 treat as unknown and skip scaling.
return count, size
}
avgSize := float64(size) / float64(count)
scale := 1 / (1 - math.Exp(-avgSize/float64(rate)))
return int64(float64(count) * scale), int64(float64(size) * scale)
}
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