2018-23-01 Paul Thomas <pault@gcc.gnu.org>

[official-gcc.git] / libgo / go / testing / benchmark.go

// 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"
        "internal/race"
        "os"
        "runtime"
        "sync"
        "sync/atomic"
        "time"
)

var matchBenchmarks = flag.String("test.bench", "", "run only benchmarks matching `regexp`")
var benchTime = flag.Duration("test.benchtime", 1*time.Second, "run each benchmark for duration `d`")
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
        importPath       string // import path of the package containing the benchmark
        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
        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.Since(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.raceErrors = -race.Errors()
        b.N = n
        b.parallelism = 1
        b.ResetTimer()
        b.StartTimer()
        b.benchFunc(b)
        b.StopTimer()
        b.previousN = n
        b.previousDuration = b.duration
        b.raceErrors += race.Errors()
        if b.raceErrors > 0 {
                b.Errorf("race detected during execution of benchmark")
        }
}

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 atomic.LoadInt32(&b.hasSub) != 0 || 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
}

var labelsOnce sync.Once

// run executes the benchmark in a separate goroutine, including all of its
// subbenchmarks. b must not have subbenchmarks.
func (b *B) run() {
        labelsOnce.Do(func() {
                fmt.Fprintf(b.w, "goos: %s\n", runtime.GOOS)
                fmt.Fprintf(b.w, "goarch: %s\n", runtime.GOARCH)
                if b.importPath != "" {
                        fmt.Fprintf(b.w, "pkg: %s\n", b.importPath)
                }
        })
        if b.context != nil {
                // Running go test --test.bench
                b.context.processBench(b) // Must call doBench.
        } else {
                // Running func Benchmark.
                b.doBench()
        }
}

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.
                n = int(d.Nanoseconds())
                if nsop := b.nsPerOp(); nsop != 0 {
                        n /= int(nsop)
                }
                // 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()
}

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

// AllocedBytesPerOp returns r.MemBytes / 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)
}

// MemString returns r.AllocedBytesPerOp and r.AllocsPerOp in the same format as 'go test'.
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) {
        runBenchmarks("", matchString, benchmarks)
}

func runBenchmarks(importPath string, 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,
                },
                importPath: importPath,
                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 {
                for j := uint(0); j < *count; j++ {
                        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 || j > 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.
        atomic.StoreInt32(&b.hasSub, 1)
        benchmarkLock.Unlock()
        defer benchmarkLock.Lock()

        benchName, ok, partial := b.name, true, false
        if b.context != nil {
                benchName, ok, partial = 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,
                },
                importPath: b.importPath,
                benchFunc:  f,
                benchTime:  b.benchTime,
                context:    b.context,
        }
        if partial {
                // Partial name match, like -bench=X/Y matching BenchmarkX.
                // Only process sub-benchmarks, if any.
                atomic.StoreInt32(&sub.hasSub, 1)
        }
        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() {
                b.run()
        }
        return b.result
}

type discard struct{}

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