1 files changed, 314 insertions, 0 deletions
diff --git a/test/heapsampling.go b/test/heapsampling.go
new file mode 100644
index 0000000..741db74
--- /dev/null
+++ b/test/heapsampling.go
@@ -0,0 +1,314 @@
+// 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)
+}