bench.go

Documentation: cmd/link/internal/benchmark

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package benchmark provides a Metrics object that enables memory and CPU
     6  // profiling for the linker. The Metrics objects can be used to mark stages
     7  // of the code, and name the measurements during that stage. There is also
     8  // optional GCs that can be performed at the end of each stage, so you
     9  // can get an accurate measurement of how each stage changes live memory.
    10  package benchmark
    11  
    12  import (
    13  	"fmt"
    14  	"io"
    15  	"os"
    16  	"runtime"
    17  	"runtime/pprof"
    18  	"time"
    19  	"unicode"
    20  )
    21  
    22  type Flags int
    23  
    24  const (
    25  	GC         = 1 << iota
    26  	NoGC Flags = 0
    27  )
    28  
    29  type Metrics struct {
    30  	gc        Flags
    31  	marks     []*mark
    32  	curMark   *mark
    33  	filebase  string
    34  	pprofFile *os.File
    35  }
    36  
    37  type mark struct {
    38  	name              string
    39  	startM, endM, gcM runtime.MemStats
    40  	startT, endT      time.Time
    41  }
    42  
    43  // New creates a new Metrics object.
    44  //
    45  // Typical usage should look like:
    46  //
    47  // func main() {
    48  //   filename := "" // Set to enable per-phase pprof file output.
    49  //   bench := benchmark.New(benchmark.GC, filename)
    50  //   defer bench.Report(os.Stdout)
    51  //   // etc
    52  //   bench.Start("foo")
    53  //   foo()
    54  //   bench.Start("bar")
    55  //   bar()
    56  // }
    57  //
    58  // Note that a nil Metrics object won't cause any errors, so one could write
    59  // code like:
    60  //
    61  //  func main() {
    62  //    enableBenchmarking := flag.Bool("enable", true, "enables benchmarking")
    63  //    flag.Parse()
    64  //    var bench *benchmark.Metrics
    65  //    if *enableBenchmarking {
    66  //      bench = benchmark.New(benchmark.GC)
    67  //    }
    68  //    bench.Start("foo")
    69  //    // etc.
    70  //  }
    71  func New(gc Flags, filebase string) *Metrics {
    72  	if gc == GC {
    73  		runtime.GC()
    74  	}
    75  	return &Metrics{gc: gc, filebase: filebase}
    76  }
    77  
    78  // Report reports the metrics.
    79  // Closes the currently Start(ed) range, and writes the report to the given io.Writer.
    80  func (m *Metrics) Report(w io.Writer) {
    81  	if m == nil {
    82  		return
    83  	}
    84  
    85  	m.closeMark()
    86  
    87  	gcString := ""
    88  	if m.gc == GC {
    89  		gcString = "_GC"
    90  	}
    91  
    92  	var totTime time.Duration
    93  	for _, curMark := range m.marks {
    94  		dur := curMark.endT.Sub(curMark.startT)
    95  		totTime += dur
    96  		fmt.Fprintf(w, "%s 1 %d ns/op", makeBenchString(curMark.name+gcString), dur.Nanoseconds())
    97  		fmt.Fprintf(w, "\t%d B/op", curMark.endM.TotalAlloc-curMark.startM.TotalAlloc)
    98  		fmt.Fprintf(w, "\t%d allocs/op", curMark.endM.Mallocs-curMark.startM.Mallocs)
    99  		if m.gc == GC {
   100  			fmt.Fprintf(w, "\t%d live-B", curMark.gcM.HeapAlloc)
   101  		} else {
   102  			fmt.Fprintf(w, "\t%d heap-B", curMark.endM.HeapAlloc)
   103  		}
   104  		fmt.Fprintf(w, "\n")
   105  	}
   106  	fmt.Fprintf(w, "%s 1 %d ns/op\n", makeBenchString("total time"+gcString), totTime.Nanoseconds())
   107  }
   108  
   109  // Starts marks the beginning of a new measurement phase.
   110  // Once a metric is started, it continues until either a Report is issued, or another Start is called.
   111  func (m *Metrics) Start(name string) {
   112  	if m == nil {
   113  		return
   114  	}
   115  	m.closeMark()
   116  	m.curMark = &mark{name: name}
   117  	// Unlikely we need to a GC here, as one was likely just done in closeMark.
   118  	if m.shouldPProf() {
   119  		f, err := os.Create(makePProfFilename(m.filebase, name, "cpuprof"))
   120  		if err != nil {
   121  			panic(err)
   122  		}
   123  		m.pprofFile = f
   124  		if err = pprof.StartCPUProfile(m.pprofFile); err != nil {
   125  			panic(err)
   126  		}
   127  	}
   128  	runtime.ReadMemStats(&m.curMark.startM)
   129  	m.curMark.startT = time.Now()
   130  }
   131  
   132  func (m *Metrics) closeMark() {
   133  	if m == nil || m.curMark == nil {
   134  		return
   135  	}
   136  	m.curMark.endT = time.Now()
   137  	if m.shouldPProf() {
   138  		pprof.StopCPUProfile()
   139  		m.pprofFile.Close()
   140  		m.pprofFile = nil
   141  	}
   142  	runtime.ReadMemStats(&m.curMark.endM)
   143  	if m.gc == GC {
   144  		runtime.GC()
   145  		runtime.ReadMemStats(&m.curMark.gcM)
   146  		if m.shouldPProf() {
   147  			// Collect a profile of the live heap. Do a
   148  			// second GC to force sweep completion so we
   149  			// get a complete snapshot of the live heap at
   150  			// the end of this phase.
   151  			runtime.GC()
   152  			f, err := os.Create(makePProfFilename(m.filebase, m.curMark.name, "memprof"))
   153  			if err != nil {
   154  				panic(err)
   155  			}
   156  			err = pprof.WriteHeapProfile(f)
   157  			if err != nil {
   158  				panic(err)
   159  			}
   160  			err = f.Close()
   161  			if err != nil {
   162  				panic(err)
   163  			}
   164  		}
   165  	}
   166  	m.marks = append(m.marks, m.curMark)
   167  	m.curMark = nil
   168  }
   169  
   170  // shouldPProf returns true if we should be doing pprof runs.
   171  func (m *Metrics) shouldPProf() bool {
   172  	return m != nil && len(m.filebase) > 0
   173  }
   174  
   175  // makeBenchString makes a benchmark string consumable by Go's benchmarking tools.
   176  func makeBenchString(name string) string {
   177  	needCap := true
   178  	ret := []rune("Benchmark")
   179  	for _, r := range name {
   180  		if unicode.IsSpace(r) {
   181  			needCap = true
   182  			continue
   183  		}
   184  		if needCap {
   185  			r = unicode.ToUpper(r)
   186  			needCap = false
   187  		}
   188  		ret = append(ret, r)
   189  	}
   190  	return string(ret)
   191  }
   192  
   193  func makePProfFilename(filebase, name, typ string) string {
   194  	return fmt.Sprintf("%s_%s.%s", filebase, makeBenchString(name), typ)
   195  }
   196
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