go/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 = 100000
	// 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.
	}
}

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 = 100000
	// 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)
	}
}

// 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)
}