src/testing/benchmark.go - go - Git at Google

 // 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.

 package testing

 import (
 	"flag"
 	"fmt"
 	"os"
 	"runtime"
 	"sync"
 	"sync/atomic"
 	"time"
 )

 var matchBenchmarks = flag.String("test.bench", "", "regular expression per path component to select benchmarks to run")
 var benchTime = flag.Duration("test.benchtime", 1*time.Second, "approximate run time for each benchmark")
 var benchmarkMemory = flag.Bool("test.benchmem", false, "print memory allocations for benchmarks")

 // Global lock to ensure only one benchmark runs at a time.
 var benchmarkLock sync.Mutex

 // Used for every benchmark for measuring memory.
 var memStats runtime.MemStats

 // An internal type but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 type InternalBenchmark struct {
 	Name string
 	F    func(b *B)
 }

 // B is a type passed to Benchmark functions to manage benchmark
 // timing and to specify the number of iterations to run.
 //
 // A benchmark ends when its Benchmark function returns or calls any of the methods
 // FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods must be called
 // only from the goroutine running the Benchmark function.
 // The other reporting methods, such as the variations of Log and Error,
 // may be called simultaneously from multiple goroutines.
 //
 // Like in tests, benchmark logs are accumulated during execution
 // and dumped to standard error when done. Unlike in tests, benchmark logs
 // are always printed, so as not to hide output whose existence may be
 // affecting benchmark results.
 type B struct {
 	common
 	context          *benchContext
 	N                int
 	previousN        int           // number of iterations in the previous run
 	previousDuration time.Duration // total duration of the previous run
 	benchFunc        func(b *B)
 	benchTime        time.Duration
 	bytes            int64
 	missingBytes     bool // one of the subbenchmarks does not have bytes set.
 	timerOn          bool
 	showAllocResult  bool
 	hasSub           bool
 	result           BenchmarkResult
 	parallelism      int // RunParallel creates parallelism*GOMAXPROCS goroutines
 	// The initial states of memStats.Mallocs and memStats.TotalAlloc.
 	startAllocs uint64
 	startBytes  uint64
 	// The net total of this test after being run.
 	netAllocs uint64
 	netBytes  uint64
 }

 // StartTimer starts timing a test. This function is called automatically
 // before a benchmark starts, but it can also used to resume timing after
 // a call to StopTimer.
 func (b *B) StartTimer() {
 	if !b.timerOn {
 		runtime.ReadMemStats(&memStats)
 		b.startAllocs = memStats.Mallocs
 		b.startBytes = memStats.TotalAlloc
 		b.start = time.Now()
 		b.timerOn = true
 	}
 }

 // StopTimer stops timing a test. This can be used to pause the timer
 // while performing complex initialization that you don't
 // want to measure.
 func (b *B) StopTimer() {
 	if b.timerOn {
 		b.duration += time.Now().Sub(b.start)
 		runtime.ReadMemStats(&memStats)
 		b.netAllocs += memStats.Mallocs - b.startAllocs
 		b.netBytes += memStats.TotalAlloc - b.startBytes
 		b.timerOn = false
 	}
 }

 // ResetTimer zeros the elapsed benchmark time and memory allocation counters.
 // It does not affect whether the timer is running.
 func (b *B) ResetTimer() {
 	if b.timerOn {
 		runtime.ReadMemStats(&memStats)
 		b.startAllocs = memStats.Mallocs
 		b.startBytes = memStats.TotalAlloc
 		b.start = time.Now()
 	}
 	b.duration = 0
 	b.netAllocs = 0
 	b.netBytes = 0
 }

 // SetBytes records the number of bytes processed in a single operation.
 // If this is called, the benchmark will report ns/op and MB/s.
 func (b *B) SetBytes(n int64) { b.bytes = n }

 // ReportAllocs enables malloc statistics for this benchmark.
 // It is equivalent to setting -test.benchmem, but it only affects the
 // benchmark function that calls ReportAllocs.
 func (b *B) ReportAllocs() {
 	b.showAllocResult = true
 }

 func (b *B) nsPerOp() int64 {
 	if b.N <= 0 {
 		return 0
 	}
 	return b.duration.Nanoseconds() / int64(b.N)
 }

 // runN runs a single benchmark for the specified number of iterations.
 func (b *B) runN(n int) {
 	benchmarkLock.Lock()
 	defer benchmarkLock.Unlock()
 	// Try to get a comparable environment for each run
 	// by clearing garbage from previous runs.
 	runtime.GC()
 	b.N = n
 	b.parallelism = 1
 	b.ResetTimer()
 	b.StartTimer()
 	b.benchFunc(b)
 	b.StopTimer()
 	b.previousN = n
 	b.previousDuration = b.duration
 }

 func min(x, y int) int {
 	if x > y {
 		return y
 	}
 	return x
 }

 func max(x, y int) int {
 	if x < y {
 		return y
 	}
 	return x
 }

 // roundDown10 rounds a number down to the nearest power of 10.
 func roundDown10(n int) int {
 	var tens = 0
 	// tens = floor(log_10(n))
 	for n >= 10 {
 		n = n / 10
 		tens++
 	}
 	// result = 10^tens
 	result := 1
 	for i := 0; i < tens; i++ {
 		result *= 10
 	}
 	return result
 }

 // roundUp rounds x up to a number of the form [1eX, 2eX, 3eX, 5eX].
 func roundUp(n int) int {
 	base := roundDown10(n)
 	switch {
 	case n <= base:
 		return base
 	case n <= (2 * base):
 		return 2 * base
 	case n <= (3 * base):
 		return 3 * base
 	case n <= (5 * base):
 		return 5 * base
 	default:
 		return 10 * base
 	}
 }

 // run1 runs the first iteration of benchFunc. It returns whether more
 // iterations of this benchmarks should be run.
 func (b *B) run1() bool {
 	if ctx := b.context; ctx != nil {
 		// Extend maxLen, if needed.
 		if n := len(b.name) + ctx.extLen + 1; n > ctx.maxLen {
 			ctx.maxLen = n + 8 // Add additional slack to avoid too many jumps in size.
 		}
 	}
 	go func() {
 		// Signal that we're done whether we return normally
 		// or by FailNow's runtime.Goexit.
 		defer func() {
 			b.signal <- true
 		}()

 		b.runN(1)
 	}()
 	<-b.signal
 	if b.failed {
 		fmt.Fprintf(b.w, "--- FAIL: %s\n%s", b.name, b.output)
 		return false
 	}
 	// Only print the output if we know we are not going to proceed.
 	// Otherwise it is printed in processBench.
 	if b.hasSub || b.finished {
 		tag := "BENCH"
 		if b.skipped {
 			tag = "SKIP"
 		}
 		if b.chatty && (len(b.output) > 0 || b.finished) {
 			b.trimOutput()
 			fmt.Fprintf(b.w, "--- %s: %s\n%s", tag, b.name, b.output)
 		}
 		return false
 	}
 	return true
 }

 // run executes the benchmark in a separate goroutine, including all of its
 // subbenchmarks. b must not have subbenchmarks.
 func (b *B) run() BenchmarkResult {
 	if b.context != nil {
 		// Running go test --test.bench
 		b.context.processBench(b) // Must call doBench.
 	} else {
 		// Running func Benchmark.
 		b.doBench()
 	}
 	return b.result
 }

 func (b *B) doBench() BenchmarkResult {
 	go b.launch()
 	<-b.signal
 	return b.result
 }

 // launch launches the benchmark function. It gradually increases the number
 // of benchmark iterations until the benchmark runs for the requested benchtime.
 // launch is run by the doBench function as a separate goroutine.
 // run1 must have been called on b.
 func (b *B) launch() {
 	// Signal that we're done whether we return normally
 	// or by FailNow's runtime.Goexit.
 	defer func() {
 		b.signal <- true
 	}()

 	// Run the benchmark for at least the specified amount of time.
 	d := b.benchTime
 	for n := 1; !b.failed && b.duration < d && n < 1e9; {
 		last := n
 		// Predict required iterations.
 		if b.nsPerOp() == 0 {
 			n = 1e9
 		} else {
 			n = int(d.Nanoseconds() / b.nsPerOp())
 		}
 		// Run more iterations than we think we'll need (1.2x).
 		// Don't grow too fast in case we had timing errors previously.
 		// Be sure to run at least one more than last time.
 		n = max(min(n+n/5, 100*last), last+1)
 		// Round up to something easy to read.
 		n = roundUp(n)
 		b.runN(n)
 	}
 	b.result = BenchmarkResult{b.N, b.duration, b.bytes, b.netAllocs, b.netBytes}
 }

 // The results of a benchmark run.
 type BenchmarkResult struct {
 	N         int           // The number of iterations.
 	T         time.Duration // The total time taken.
 	Bytes     int64         // Bytes processed in one iteration.
 	MemAllocs uint64        // The total number of memory allocations.
 	MemBytes  uint64        // The total number of bytes allocated.
 }

 func (r BenchmarkResult) NsPerOp() int64 {
 	if r.N <= 0 {
 		return 0
 	}
 	return r.T.Nanoseconds() / int64(r.N)
 }

 func (r BenchmarkResult) mbPerSec() float64 {
 	if r.Bytes <= 0 || r.T <= 0 || r.N <= 0 {
 		return 0
 	}
 	return (float64(r.Bytes) * float64(r.N) / 1e6) / r.T.Seconds()
 }

 func (r BenchmarkResult) AllocsPerOp() int64 {
 	if r.N <= 0 {
 		return 0
 	}
 	return int64(r.MemAllocs) / int64(r.N)
 }

 func (r BenchmarkResult) AllocedBytesPerOp() int64 {
 	if r.N <= 0 {
 		return 0
 	}
 	return int64(r.MemBytes) / int64(r.N)
 }

 func (r BenchmarkResult) String() string {
 	mbs := r.mbPerSec()
 	mb := ""
 	if mbs != 0 {
 		mb = fmt.Sprintf("\t%7.2f MB/s", mbs)
 	}
 	nsop := r.NsPerOp()
 	ns := fmt.Sprintf("%10d ns/op", nsop)
 	if r.N > 0 && nsop < 100 {
 		// The format specifiers here make sure that
 		// the ones digits line up for all three possible formats.
 		if nsop < 10 {
 			ns = fmt.Sprintf("%13.2f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
 		} else {
 			ns = fmt.Sprintf("%12.1f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
 		}
 	}
 	return fmt.Sprintf("%8d\t%s%s", r.N, ns, mb)
 }

 func (r BenchmarkResult) MemString() string {
 	return fmt.Sprintf("%8d B/op\t%8d allocs/op",
 		r.AllocedBytesPerOp(), r.AllocsPerOp())
 }

 // benchmarkName returns full name of benchmark including procs suffix.
 func benchmarkName(name string, n int) string {
 	if n != 1 {
 		return fmt.Sprintf("%s-%d", name, n)
 	}
 	return name
 }

 type benchContext struct {
 	match *matcher

 	maxLen int // The largest recorded benchmark name.
 	extLen int // Maximum extension length.
 }

 // An internal function but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
 	runBenchmarksInternal(matchString, benchmarks)
 }

 func runBenchmarksInternal(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) bool {
 	// If no flag was specified, don't run benchmarks.
 	if len(*matchBenchmarks) == 0 {
 		return true
 	}
 	// Collect matching benchmarks and determine longest name.
 	maxprocs := 1
 	for _, procs := range cpuList {
 		if procs > maxprocs {
 			maxprocs = procs
 		}
 	}
 	ctx := &benchContext{
 		match:  newMatcher(matchString, *matchBenchmarks, "-test.bench"),
 		extLen: len(benchmarkName("", maxprocs)),
 	}
 	var bs []InternalBenchmark
 	for _, Benchmark := range benchmarks {
 		if _, matched := ctx.match.fullName(nil, Benchmark.Name); matched {
 			bs = append(bs, Benchmark)
 			benchName := benchmarkName(Benchmark.Name, maxprocs)
 			if l := len(benchName) + ctx.extLen + 1; l > ctx.maxLen {
 				ctx.maxLen = l
 			}
 		}
 	}
 	main := &B{
 		common: common{
 			name:   "Main",
 			w:      os.Stdout,
 			chatty: *chatty,
 		},
 		benchFunc: func(b *B) {
 			for _, Benchmark := range bs {
 				b.Run(Benchmark.Name, Benchmark.F)
 			}
 		},
 		benchTime: *benchTime,
 		context:   ctx,
 	}
 	main.runN(1)
 	return !main.failed
 }

 // processBench runs bench b for the configured CPU counts and prints the results.
 func (ctx *benchContext) processBench(b *B) {
 	for i, procs := range cpuList {
 		runtime.GOMAXPROCS(procs)
 		benchName := benchmarkName(b.name, procs)
 		fmt.Fprintf(b.w, "%-*s\t", ctx.maxLen, benchName)
 		// Recompute the running time for all but the first iteration.
 		if i > 0 {
 			b = &B{
 				common: common{
 					signal: make(chan bool),
 					name:   b.name,
 					w:      b.w,
 					chatty: b.chatty,
 				},
 				benchFunc: b.benchFunc,
 				benchTime: b.benchTime,
 			}
 			b.run1()
 		}
 		r := b.doBench()
 		if b.failed {
 			// The output could be very long here, but probably isn't.
 			// We print it all, regardless, because we don't want to trim the reason
 			// the benchmark failed.
 			fmt.Fprintf(b.w, "--- FAIL: %s\n%s", benchName, b.output)
 			continue
 		}
 		results := r.String()
 		if *benchmarkMemory || b.showAllocResult {
 			results += "\t" + r.MemString()
 		}
 		fmt.Fprintln(b.w, results)
 		// Unlike with tests, we ignore the -chatty flag and always print output for
 		// benchmarks since the output generation time will skew the results.
 		if len(b.output) > 0 {
 			b.trimOutput()
 			fmt.Fprintf(b.w, "--- BENCH: %s\n%s", benchName, b.output)
 		}
 		if p := runtime.GOMAXPROCS(-1); p != procs {
 			fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
 		}
 	}
 }

 // Run benchmarks f as a subbenchmark with the given name. It reports
 // whether there were any failures.
 //
 // A subbenchmark is like any other benchmark. A benchmark that calls Run at
 // least once will not be measured itself and will be called once with N=1.
 func (b *B) Run(name string, f func(b *B)) bool {
 	// Since b has subbenchmarks, we will no longer run it as a benchmark itself.
 	// Release the lock and acquire it on exit to ensure locks stay paired.
 	b.hasSub = true
 	benchmarkLock.Unlock()
 	defer benchmarkLock.Lock()

 	benchName, ok := b.name, true
 	if b.context != nil {
 		benchName, ok = b.context.match.fullName(&b.common, name)
 	}
 	if !ok {
 		return true
 	}
 	sub := &B{
 		common: common{
 			signal: make(chan bool),
 			name:   benchName,
 			parent: &b.common,
 			level:  b.level + 1,
 			w:      b.w,
 			chatty: b.chatty,
 		},
 		benchFunc: f,
 		benchTime: b.benchTime,
 		context:   b.context,
 	}
 	if sub.run1() {
 		sub.run()
 	}
 	b.add(sub.result)
 	return !sub.failed
 }

 // add simulates running benchmarks in sequence in a single iteration. It is
 // used to give some meaningful results in case func Benchmark is used in
 // combination with Run.
 func (b *B) add(other BenchmarkResult) {
 	r := &b.result
 	// The aggregated BenchmarkResults resemble running all subbenchmarks as
 	// in sequence in a single benchmark.
 	r.N = 1
 	r.T += time.Duration(other.NsPerOp())
 	if other.Bytes == 0 {
 		// Summing Bytes is meaningless in aggregate if not all subbenchmarks
 		// set it.
 		b.missingBytes = true
 		r.Bytes = 0
 	}
 	if !b.missingBytes {
 		r.Bytes += other.Bytes
 	}
 	r.MemAllocs += uint64(other.AllocsPerOp())
 	r.MemBytes += uint64(other.AllocedBytesPerOp())
 }

 // trimOutput shortens the output from a benchmark, which can be very long.
 func (b *B) trimOutput() {
 	// The output is likely to appear multiple times because the benchmark
 	// is run multiple times, but at least it will be seen. This is not a big deal
 	// because benchmarks rarely print, but just in case, we trim it if it's too long.
 	const maxNewlines = 10
 	for nlCount, j := 0, 0; j < len(b.output); j++ {
 		if b.output[j] == '\n' {
 			nlCount++
 			if nlCount >= maxNewlines {
 				b.output = append(b.output[:j], "\n\t... [output truncated]\n"...)
 				break
 			}
 		}
 	}
 }

 // A PB is used by RunParallel for running parallel benchmarks.
 type PB struct {
 	globalN *uint64 // shared between all worker goroutines iteration counter
 	grain   uint64  // acquire that many iterations from globalN at once
 	cache   uint64  // local cache of acquired iterations
 	bN      uint64  // total number of iterations to execute (b.N)
 }

 // Next reports whether there are more iterations to execute.
 func (pb *PB) Next() bool {
 	if pb.cache == 0 {
 		n := atomic.AddUint64(pb.globalN, pb.grain)
 		if n <= pb.bN {
 			pb.cache = pb.grain
 		} else if n < pb.bN+pb.grain {
 			pb.cache = pb.bN + pb.grain - n
 		} else {
 			return false
 		}
 	}
 	pb.cache--
 	return true
 }

 // RunParallel runs a benchmark in parallel.
 // It creates multiple goroutines and distributes b.N iterations among them.
 // The number of goroutines defaults to GOMAXPROCS. To increase parallelism for
 // non-CPU-bound benchmarks, call SetParallelism before RunParallel.
 // RunParallel is usually used with the go test -cpu flag.
 //
 // The body function will be run in each goroutine. It should set up any
 // goroutine-local state and then iterate until pb.Next returns false.
 // It should not use the StartTimer, StopTimer, or ResetTimer functions,
 // because they have global effect. It should also not call Run.
 func (b *B) RunParallel(body func(*PB)) {
 	if b.N == 0 {
 		return // Nothing to do when probing.
 	}
 	// Calculate grain size as number of iterations that take ~100µs.
 	// 100µs is enough to amortize the overhead and provide sufficient
 	// dynamic load balancing.
 	grain := uint64(0)
 	if b.previousN > 0 && b.previousDuration > 0 {
 		grain = 1e5 * uint64(b.previousN) / uint64(b.previousDuration)
 	}
 	if grain < 1 {
 		grain = 1
 	}
 	// We expect the inner loop and function call to take at least 10ns,
 	// so do not do more than 100µs/10ns=1e4 iterations.
 	if grain > 1e4 {
 		grain = 1e4
 	}

 	n := uint64(0)
 	numProcs := b.parallelism * runtime.GOMAXPROCS(0)
 	var wg sync.WaitGroup
 	wg.Add(numProcs)
 	for p := 0; p < numProcs; p++ {
 		go func() {
 			defer wg.Done()
 			pb := &PB{
 				globalN: &n,
 				grain:   grain,
 				bN:      uint64(b.N),
 			}
 			body(pb)
 		}()
 	}
 	wg.Wait()
 	if n <= uint64(b.N) && !b.Failed() {
 		b.Fatal("RunParallel: body exited without pb.Next() == false")
 	}
 }

 // SetParallelism sets the number of goroutines used by RunParallel to p*GOMAXPROCS.
 // There is usually no need to call SetParallelism for CPU-bound benchmarks.
 // If p is less than 1, this call will have no effect.
 func (b *B) SetParallelism(p int) {
 	if p >= 1 {
 		b.parallelism = p
 	}
 }

 // Benchmark benchmarks a single function. Useful for creating
 // custom benchmarks that do not use the "go test" command.
 //
 // If f calls Run, the result will be an estimate of running all its
 // subbenchmarks that don't call Run in sequence in a single benchmark.
 func Benchmark(f func(b *B)) BenchmarkResult {
 	b := &B{
 		common: common{
 			signal: make(chan bool),
 			w:      discard{},
 		},
 		benchFunc: f,
 		benchTime: *benchTime,
 	}
 	if !b.run1() {
 		return BenchmarkResult{}
 	}
 	return b.run()
 }

 type discard struct{}

 func (discard) Write(b []byte) (n int, err error) { return len(b), nil }
	// 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.

	package testing

	import (
	"flag"
	"fmt"
	"os"
	"runtime"
	"sync"
	"sync/atomic"
	"time"
	)

	var matchBenchmarks = flag.String("test.bench", "", "regular expression per path component to select benchmarks to run")
	var benchTime = flag.Duration("test.benchtime", 1*time.Second, "approximate run time for each benchmark")
	var benchmarkMemory = flag.Bool("test.benchmem", false, "print memory allocations for benchmarks")

	// Global lock to ensure only one benchmark runs at a time.
	var benchmarkLock sync.Mutex

	// Used for every benchmark for measuring memory.
	var memStats runtime.MemStats

	// An internal type but exported because it is cross-package; part of the implementation
	// of the "go test" command.
	type InternalBenchmark struct {
	Name string
	F func(b *B)
	}

	// B is a type passed to Benchmark functions to manage benchmark
	// timing and to specify the number of iterations to run.
	//
	// A benchmark ends when its Benchmark function returns or calls any of the methods
	// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods must be called
	// only from the goroutine running the Benchmark function.
	// The other reporting methods, such as the variations of Log and Error,
	// may be called simultaneously from multiple goroutines.
	//
	// Like in tests, benchmark logs are accumulated during execution
	// and dumped to standard error when done. Unlike in tests, benchmark logs
	// are always printed, so as not to hide output whose existence may be
	// affecting benchmark results.
	type B struct {
	common
	context *benchContext
	N int
	previousN int // number of iterations in the previous run
	previousDuration time.Duration // total duration of the previous run
	benchFunc func(b *B)
	benchTime time.Duration
	bytes int64
	missingBytes bool // one of the subbenchmarks does not have bytes set.
	timerOn bool
	showAllocResult bool
	hasSub bool
	result BenchmarkResult
	parallelism int // RunParallel creates parallelism*GOMAXPROCS goroutines
	// The initial states of memStats.Mallocs and memStats.TotalAlloc.
	startAllocs uint64
	startBytes uint64
	// The net total of this test after being run.
	netAllocs uint64
	netBytes uint64
	}

	// StartTimer starts timing a test. This function is called automatically
	// before a benchmark starts, but it can also used to resume timing after
	// a call to StopTimer.
	func (b *B) StartTimer() {
	if !b.timerOn {
	runtime.ReadMemStats(&memStats)
	b.startAllocs = memStats.Mallocs
	b.startBytes = memStats.TotalAlloc
	b.start = time.Now()
	b.timerOn = true
	}
	}

	// StopTimer stops timing a test. This can be used to pause the timer
	// while performing complex initialization that you don't
	// want to measure.
	func (b *B) StopTimer() {
	if b.timerOn {
	b.duration += time.Now().Sub(b.start)
	runtime.ReadMemStats(&memStats)
	b.netAllocs += memStats.Mallocs - b.startAllocs
	b.netBytes += memStats.TotalAlloc - b.startBytes
	b.timerOn = false
	}
	}

	// ResetTimer zeros the elapsed benchmark time and memory allocation counters.
	// It does not affect whether the timer is running.
	func (b *B) ResetTimer() {
	if b.timerOn {
	runtime.ReadMemStats(&memStats)
	b.startAllocs = memStats.Mallocs
	b.startBytes = memStats.TotalAlloc
	b.start = time.Now()
	}
	b.duration = 0
	b.netAllocs = 0
	b.netBytes = 0
	}

	// SetBytes records the number of bytes processed in a single operation.
	// If this is called, the benchmark will report ns/op and MB/s.
	func (b *B) SetBytes(n int64) { b.bytes = n }

	// ReportAllocs enables malloc statistics for this benchmark.
	// It is equivalent to setting -test.benchmem, but it only affects the
	// benchmark function that calls ReportAllocs.
	func (b *B) ReportAllocs() {
	b.showAllocResult = true
	}

	func (b *B) nsPerOp() int64 {
	if b.N <= 0 {
	return 0
	}
	return b.duration.Nanoseconds() / int64(b.N)
	}

	// runN runs a single benchmark for the specified number of iterations.
	func (b *B) runN(n int) {
	benchmarkLock.Lock()
	defer benchmarkLock.Unlock()
	// Try to get a comparable environment for each run
	// by clearing garbage from previous runs.
	runtime.GC()
	b.N = n
	b.parallelism = 1
	b.ResetTimer()
	b.StartTimer()
	b.benchFunc(b)
	b.StopTimer()
	b.previousN = n
	b.previousDuration = b.duration
	}

	func min(x, y int) int {
	if x > y {
	return y
	}
	return x
	}

	func max(x, y int) int {
	if x < y {
	return y
	}
	return x
	}

	// roundDown10 rounds a number down to the nearest power of 10.
	func roundDown10(n int) int {
	var tens = 0
	// tens = floor(log_10(n))
	for n >= 10 {
	n = n / 10
	tens++
	}
	// result = 10^tens
	result := 1
	for i := 0; i < tens; i++ {
	result *= 10
	}
	return result
	}

	// roundUp rounds x up to a number of the form [1eX, 2eX, 3eX, 5eX].
	func roundUp(n int) int {
	base := roundDown10(n)
	switch {
	case n <= base:
	return base
	case n <= (2 * base):
	return 2 * base
	case n <= (3 * base):
	return 3 * base
	case n <= (5 * base):
	return 5 * base
	default:
	return 10 * base
	}
	}

	// run1 runs the first iteration of benchFunc. It returns whether more
	// iterations of this benchmarks should be run.
	func (b *B) run1() bool {
	if ctx := b.context; ctx != nil {
	// Extend maxLen, if needed.
	if n := len(b.name) + ctx.extLen + 1; n > ctx.maxLen {
	ctx.maxLen = n + 8 // Add additional slack to avoid too many jumps in size.
	}
	}
	go func() {
	// Signal that we're done whether we return normally
	// or by FailNow's runtime.Goexit.
	defer func() {
	b.signal <- true
	}()

	b.runN(1)
	}()
	<-b.signal
	if b.failed {
	fmt.Fprintf(b.w, "--- FAIL: %s\n%s", b.name, b.output)
	return false
	}
	// Only print the output if we know we are not going to proceed.
	// Otherwise it is printed in processBench.
	if b.hasSub \|\| b.finished {
	tag := "BENCH"
	if b.skipped {
	tag = "SKIP"
	}
	if b.chatty && (len(b.output) > 0 \|\| b.finished) {
	b.trimOutput()
	fmt.Fprintf(b.w, "--- %s: %s\n%s", tag, b.name, b.output)
	}
	return false
	}
	return true
	}

	// run executes the benchmark in a separate goroutine, including all of its
	// subbenchmarks. b must not have subbenchmarks.
	func (b *B) run() BenchmarkResult {
	if b.context != nil {
	// Running go test --test.bench
	b.context.processBench(b) // Must call doBench.
	} else {
	// Running func Benchmark.
	b.doBench()
	}
	return b.result
	}

	func (b *B) doBench() BenchmarkResult {
	go b.launch()
	<-b.signal
	return b.result
	}

	// launch launches the benchmark function. It gradually increases the number
	// of benchmark iterations until the benchmark runs for the requested benchtime.
	// launch is run by the doBench function as a separate goroutine.
	// run1 must have been called on b.
	func (b *B) launch() {
	// Signal that we're done whether we return normally
	// or by FailNow's runtime.Goexit.
	defer func() {
	b.signal <- true
	}()

	// Run the benchmark for at least the specified amount of time.
	d := b.benchTime
	for n := 1; !b.failed && b.duration < d && n < 1e9; {
	last := n
	// Predict required iterations.
	if b.nsPerOp() == 0 {
	n = 1e9
	} else {
	n = int(d.Nanoseconds() / b.nsPerOp())
	}
	// Run more iterations than we think we'll need (1.2x).
	// Don't grow too fast in case we had timing errors previously.
	// Be sure to run at least one more than last time.
	n = max(min(n+n/5, 100*last), last+1)
	// Round up to something easy to read.
	n = roundUp(n)
	b.runN(n)
	}
	b.result = BenchmarkResult{b.N, b.duration, b.bytes, b.netAllocs, b.netBytes}
	}

	// The results of a benchmark run.
	type BenchmarkResult struct {
	N int // The number of iterations.
	T time.Duration // The total time taken.
	Bytes int64 // Bytes processed in one iteration.
	MemAllocs uint64 // The total number of memory allocations.
	MemBytes uint64 // The total number of bytes allocated.
	}

	func (r BenchmarkResult) NsPerOp() int64 {
	if r.N <= 0 {
	return 0
	}
	return r.T.Nanoseconds() / int64(r.N)
	}

	func (r BenchmarkResult) mbPerSec() float64 {
	if r.Bytes <= 0 \|\| r.T <= 0 \|\| r.N <= 0 {
	return 0
	}
	return (float64(r.Bytes) * float64(r.N) / 1e6) / r.T.Seconds()
	}

	func (r BenchmarkResult) AllocsPerOp() int64 {
	if r.N <= 0 {
	return 0
	}
	return int64(r.MemAllocs) / int64(r.N)
	}

	func (r BenchmarkResult) AllocedBytesPerOp() int64 {
	if r.N <= 0 {
	return 0
	}
	return int64(r.MemBytes) / int64(r.N)
	}

	func (r BenchmarkResult) String() string {
	mbs := r.mbPerSec()
	mb := ""
	if mbs != 0 {
	mb = fmt.Sprintf("\t%7.2f MB/s", mbs)
	}
	nsop := r.NsPerOp()
	ns := fmt.Sprintf("%10d ns/op", nsop)
	if r.N > 0 && nsop < 100 {
	// The format specifiers here make sure that
	// the ones digits line up for all three possible formats.
	if nsop < 10 {
	ns = fmt.Sprintf("%13.2f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
	} else {
	ns = fmt.Sprintf("%12.1f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
	}
	}
	return fmt.Sprintf("%8d\t%s%s", r.N, ns, mb)
	}

	func (r BenchmarkResult) MemString() string {
	return fmt.Sprintf("%8d B/op\t%8d allocs/op",
	r.AllocedBytesPerOp(), r.AllocsPerOp())
	}

	// benchmarkName returns full name of benchmark including procs suffix.
	func benchmarkName(name string, n int) string {
	if n != 1 {
	return fmt.Sprintf("%s-%d", name, n)
	}
	return name
	}

	type benchContext struct {
	match *matcher

	maxLen int // The largest recorded benchmark name.
	extLen int // Maximum extension length.
	}

	// An internal function but exported because it is cross-package; part of the implementation
	// of the "go test" command.
	func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
	runBenchmarksInternal(matchString, benchmarks)
	}

	func runBenchmarksInternal(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) bool {
	// If no flag was specified, don't run benchmarks.
	if len(*matchBenchmarks) == 0 {
	return true
	}
	// Collect matching benchmarks and determine longest name.
	maxprocs := 1
	for _, procs := range cpuList {
	if procs > maxprocs {
	maxprocs = procs
	}
	}
	ctx := &benchContext{
	match: newMatcher(matchString, *matchBenchmarks, "-test.bench"),
	extLen: len(benchmarkName("", maxprocs)),
	}
	var bs []InternalBenchmark
	for _, Benchmark := range benchmarks {
	if _, matched := ctx.match.fullName(nil, Benchmark.Name); matched {
	bs = append(bs, Benchmark)
	benchName := benchmarkName(Benchmark.Name, maxprocs)
	if l := len(benchName) + ctx.extLen + 1; l > ctx.maxLen {
	ctx.maxLen = l
	}
	}
	}
	main := &B{
	common: common{
	name: "Main",
	w: os.Stdout,
	chatty: *chatty,
	},
	benchFunc: func(b *B) {
	for _, Benchmark := range bs {
	b.Run(Benchmark.Name, Benchmark.F)
	}
	},
	benchTime: *benchTime,
	context: ctx,
	}
	main.runN(1)
	return !main.failed
	}

	// processBench runs bench b for the configured CPU counts and prints the results.
	func (ctx benchContext) processBench(b B) {
	for i, procs := range cpuList {
	runtime.GOMAXPROCS(procs)
	benchName := benchmarkName(b.name, procs)
	fmt.Fprintf(b.w, "%-*s\t", ctx.maxLen, benchName)
	// Recompute the running time for all but the first iteration.
	if i > 0 {
	b = &B{
	common: common{
	signal: make(chan bool),
	name: b.name,
	w: b.w,
	chatty: b.chatty,
	},
	benchFunc: b.benchFunc,
	benchTime: b.benchTime,
	}
	b.run1()
	}
	r := b.doBench()
	if b.failed {
	// The output could be very long here, but probably isn't.
	// We print it all, regardless, because we don't want to trim the reason
	// the benchmark failed.
	fmt.Fprintf(b.w, "--- FAIL: %s\n%s", benchName, b.output)
	continue
	}
	results := r.String()
	if *benchmarkMemory \|\| b.showAllocResult {
	results += "\t" + r.MemString()
	}
	fmt.Fprintln(b.w, results)
	// Unlike with tests, we ignore the -chatty flag and always print output for
	// benchmarks since the output generation time will skew the results.
	if len(b.output) > 0 {
	b.trimOutput()
	fmt.Fprintf(b.w, "--- BENCH: %s\n%s", benchName, b.output)
	}
	if p := runtime.GOMAXPROCS(-1); p != procs {
	fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
	}
	}
	}

	// Run benchmarks f as a subbenchmark with the given name. It reports
	// whether there were any failures.
	//
	// A subbenchmark is like any other benchmark. A benchmark that calls Run at
	// least once will not be measured itself and will be called once with N=1.
	func (b B) Run(name string, f func(b B)) bool {
	// Since b has subbenchmarks, we will no longer run it as a benchmark itself.
	// Release the lock and acquire it on exit to ensure locks stay paired.
	b.hasSub = true
	benchmarkLock.Unlock()
	defer benchmarkLock.Lock()

	benchName, ok := b.name, true
	if b.context != nil {
	benchName, ok = b.context.match.fullName(&b.common, name)
	}
	if !ok {
	return true
	}
	sub := &B{
	common: common{
	signal: make(chan bool),
	name: benchName,
	parent: &b.common,
	level: b.level + 1,
	w: b.w,
	chatty: b.chatty,
	},
	benchFunc: f,
	benchTime: b.benchTime,
	context: b.context,
	}
	if sub.run1() {
	sub.run()
	}
	b.add(sub.result)
	return !sub.failed
	}

	// add simulates running benchmarks in sequence in a single iteration. It is
	// used to give some meaningful results in case func Benchmark is used in
	// combination with Run.
	func (b *B) add(other BenchmarkResult) {
	r := &b.result
	// The aggregated BenchmarkResults resemble running all subbenchmarks as
	// in sequence in a single benchmark.
	r.N = 1
	r.T += time.Duration(other.NsPerOp())
	if other.Bytes == 0 {
	// Summing Bytes is meaningless in aggregate if not all subbenchmarks
	// set it.
	b.missingBytes = true
	r.Bytes = 0
	}
	if !b.missingBytes {
	r.Bytes += other.Bytes
	}
	r.MemAllocs += uint64(other.AllocsPerOp())
	r.MemBytes += uint64(other.AllocedBytesPerOp())
	}

	// trimOutput shortens the output from a benchmark, which can be very long.
	func (b *B) trimOutput() {
	// The output is likely to appear multiple times because the benchmark
	// is run multiple times, but at least it will be seen. This is not a big deal
	// because benchmarks rarely print, but just in case, we trim it if it's too long.
	const maxNewlines = 10
	for nlCount, j := 0, 0; j < len(b.output); j++ {
	if b.output[j] == '\n' {
	nlCount++
	if nlCount >= maxNewlines {
	b.output = append(b.output[:j], "\n\t... [output truncated]\n"...)
	break
	}
	}
	}
	}

	// A PB is used by RunParallel for running parallel benchmarks.
	type PB struct {
	globalN *uint64 // shared between all worker goroutines iteration counter
	grain uint64 // acquire that many iterations from globalN at once
	cache uint64 // local cache of acquired iterations
	bN uint64 // total number of iterations to execute (b.N)
	}

	// Next reports whether there are more iterations to execute.
	func (pb *PB) Next() bool {
	if pb.cache == 0 {
	n := atomic.AddUint64(pb.globalN, pb.grain)
	if n <= pb.bN {
	pb.cache = pb.grain
	} else if n < pb.bN+pb.grain {
	pb.cache = pb.bN + pb.grain - n
	} else {
	return false
	}
	}
	pb.cache--
	return true
	}

	// RunParallel runs a benchmark in parallel.
	// It creates multiple goroutines and distributes b.N iterations among them.
	// The number of goroutines defaults to GOMAXPROCS. To increase parallelism for
	// non-CPU-bound benchmarks, call SetParallelism before RunParallel.
	// RunParallel is usually used with the go test -cpu flag.
	//
	// The body function will be run in each goroutine. It should set up any
	// goroutine-local state and then iterate until pb.Next returns false.
	// It should not use the StartTimer, StopTimer, or ResetTimer functions,
	// because they have global effect. It should also not call Run.
	func (b B) RunParallel(body func(PB)) {
	if b.N == 0 {
	return // Nothing to do when probing.
	}
	// Calculate grain size as number of iterations that take ~100µs.
	// 100µs is enough to amortize the overhead and provide sufficient
	// dynamic load balancing.
	grain := uint64(0)
	if b.previousN > 0 && b.previousDuration > 0 {
	grain = 1e5 * uint64(b.previousN) / uint64(b.previousDuration)
	}
	if grain < 1 {
	grain = 1
	}
	// We expect the inner loop and function call to take at least 10ns,
	// so do not do more than 100µs/10ns=1e4 iterations.
	if grain > 1e4 {
	grain = 1e4
	}

	n := uint64(0)
	numProcs := b.parallelism * runtime.GOMAXPROCS(0)
	var wg sync.WaitGroup
	wg.Add(numProcs)
	for p := 0; p < numProcs; p++ {
	go func() {
	defer wg.Done()
	pb := &PB{
	globalN: &n,
	grain: grain,
	bN: uint64(b.N),
	}
	body(pb)
	}()
	}
	wg.Wait()
	if n <= uint64(b.N) && !b.Failed() {
	b.Fatal("RunParallel: body exited without pb.Next() == false")
	}
	}

	// SetParallelism sets the number of goroutines used by RunParallel to p*GOMAXPROCS.
	// There is usually no need to call SetParallelism for CPU-bound benchmarks.
	// If p is less than 1, this call will have no effect.
	func (b *B) SetParallelism(p int) {
	if p >= 1 {
	b.parallelism = p
	}
	}

	// Benchmark benchmarks a single function. Useful for creating
	// custom benchmarks that do not use the "go test" command.
	//
	// If f calls Run, the result will be an estimate of running all its
	// subbenchmarks that don't call Run in sequence in a single benchmark.
	func Benchmark(f func(b *B)) BenchmarkResult {
	b := &B{
	common: common{
	signal: make(chan bool),
	w: discard{},
	},
	benchFunc: f,
	benchTime: *benchTime,
	}
	if !b.run1() {
	return BenchmarkResult{}
	}
	return b.run()
	}

	type discard struct{}

	func (discard) Write(b []byte) (n int, err error) { return len(b), nil }