Rebase.

[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"
        "os"
        "runtime"
        "sync"
        "sync/atomic"
        "time"
)

var matchBenchmarks = flag.String("test.bench", "", "regular expression 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.
type B struct {
        common
        N                int
        previousN        int           // number of iterations in the previous run
        previousDuration time.Duration // total duration of the previous run
        benchmark        InternalBenchmark
        bytes            int64
        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.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.benchmark.F(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, 5eX].
func roundUp(n int) int {
        base := roundDown10(n)
        switch {
        case n <= base:
                return base
        case n <= (2 * base):
                return 2 * base
        case n <= (5 * base):
                return 5 * base
        default:
                return 10 * base
        }
}

// run times the benchmark function in a separate goroutine.
func (b *B) run() 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 a second in order
// to get a reasonable measurement.  It prints timing information in this form
//              testing.BenchmarkHello  100000          19 ns/op
// launch is run by the fun function as a separate goroutine.
func (b *B) launch() {
        // Run the benchmark for a single iteration in case it's expensive.
        n := 1

        // Signal that we're done whether we return normally
        // or by FailNow's runtime.Goexit.
        defer func() {
                b.signal <- b
        }()

        b.runN(n)
        // Run the benchmark for at least the specified amount of time.
        d := *benchTime
        for !b.failed && b.duration < d && n < 1e9 {
                last := n
                // Predict iterations/sec.
                if b.nsPerOp() == 0 {
                        n = 1e9
                } else {
                        n = int(d.Nanoseconds() / b.nsPerOp())
                }
                // Run more iterations than we think we'll need for a second (1.5x).
                // 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/2, 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())
}

// 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) {
        // If no flag was specified, don't run benchmarks.
        if len(*matchBenchmarks) == 0 {
                return
        }
        for _, Benchmark := range benchmarks {
                matched, err := matchString(*matchBenchmarks, Benchmark.Name)
                if err != nil {
                        fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.bench: %s\n", err)
                        os.Exit(1)
                }
                if !matched {
                        continue
                }
                for _, procs := range cpuList {
                        runtime.GOMAXPROCS(procs)
                        b := &B{
                                common: common{
                                        signal: make(chan interface{}),
                                },
                                benchmark: Benchmark,
                        }
                        benchName := Benchmark.Name
                        if procs != 1 {
                                benchName = fmt.Sprintf("%s-%d", Benchmark.Name, procs)
                        }
                        fmt.Printf("%s\t", benchName)
                        r := b.run()
                        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.Printf("--- FAIL: %s\n%s", benchName, b.output)
                                continue
                        }
                        results := r.String()
                        if *benchmarkMemory || b.showAllocResult {
                                results += "\t" + r.MemString()
                        }
                        fmt.Println(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.Printf("--- 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)
                        }
                }
        }
}

// 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.
func (b *B) RunParallel(body func(*PB)) {
        // 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.
func Benchmark(f func(b *B)) BenchmarkResult {
        b := &B{
                common: common{
                        signal: make(chan interface{}),
                },
                benchmark: InternalBenchmark{"", f},
        }
        return b.run()
}