1 files changed, 195 insertions, 0 deletions
diff --git a/src/cmd/link/internal/benchmark/bench.go b/src/cmd/link/internal/benchmark/bench.go
new file mode 100644
index 0000000000..6c163c801e
--- /dev/null
+++ b/src/cmd/link/internal/benchmark/bench.go
@@ -0,0 +1,195 @@
+// Copyright 2020 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 benchmark provides a Metrics object that enables memory and CPU
+// profiling for the linker. The Metrics objects can be used to mark stages
+// of the code, and name the measurements during that stage. There is also
+// optional GCs that can be performed at the end of each stage, so you
+// can get an accurate measurement of how each stage changes live memory.
+package benchmark
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"runtime"
+	"runtime/pprof"
+	"time"
+	"unicode"
+)
+
+type Flags int
+
+const (
+	GC         = 1 << iota
+	NoGC Flags = 0
+)
+
+type Metrics struct {
+	gc        Flags
+	marks     []*mark
+	curMark   *mark
+	filebase  string
+	pprofFile *os.File
+}
+
+type mark struct {
+	name              string
+	startM, endM, gcM runtime.MemStats
+	startT, endT      time.Time
+}
+
+// New creates a new Metrics object.
+//
+// Typical usage should look like:
+//
+// func main() {
+//   filename := "" // Set to enable per-phase pprof file output.
+//   bench := benchmark.New(benchmark.GC, filename)
+//   defer bench.Report(os.Stdout)
+//   // etc
+//   bench.Start("foo")
+//   foo()
+//   bench.Start("bar")
+//   bar()
+// }
+//
+// Note that a nil Metrics object won't cause any errors, so one could write
+// code like:
+//
+//  func main() {
+//    enableBenchmarking := flag.Bool("enable", true, "enables benchmarking")
+//    flag.Parse()
+//    var bench *benchmark.Metrics
+//    if *enableBenchmarking {
+//      bench = benchmark.New(benchmark.GC)
+//    }
+//    bench.Start("foo")
+//    // etc.
+//  }
+func New(gc Flags, filebase string) *Metrics {
+	if gc == GC {
+		runtime.GC()
+	}
+	return &Metrics{gc: gc, filebase: filebase}
+}
+
+// Report reports the metrics.
+// Closes the currently Start(ed) range, and writes the report to the given io.Writer.
+func (m *Metrics) Report(w io.Writer) {
+	if m == nil {
+		return
+	}
+
+	m.closeMark()
+
+	gcString := ""
+	if m.gc == GC {
+		gcString = "_GC"
+	}
+
+	var totTime time.Duration
+	for _, curMark := range m.marks {
+		dur := curMark.endT.Sub(curMark.startT)
+		totTime += dur
+		fmt.Fprintf(w, "%s 1 %d ns/op", makeBenchString(curMark.name+gcString), dur.Nanoseconds())
+		fmt.Fprintf(w, "\t%d B/op", curMark.endM.TotalAlloc-curMark.startM.TotalAlloc)
+		fmt.Fprintf(w, "\t%d allocs/op", curMark.endM.Mallocs-curMark.startM.Mallocs)
+		if m.gc == GC {
+			fmt.Fprintf(w, "\t%d live-B", curMark.gcM.HeapAlloc)
+		} else {
+			fmt.Fprintf(w, "\t%d heap-B", curMark.endM.HeapAlloc)
+		}
+		fmt.Fprintf(w, "\n")
+	}
+	fmt.Fprintf(w, "%s 1 %d ns/op\n", makeBenchString("total time"+gcString), totTime.Nanoseconds())
+}
+
+// Starts marks the beginning of a new measurement phase.
+// Once a metric is started, it continues until either a Report is issued, or another Start is called.
+func (m *Metrics) Start(name string) {
+	if m == nil {
+		return
+	}
+	m.closeMark()
+	m.curMark = &mark{name: name}
+	// Unlikely we need to a GC here, as one was likely just done in closeMark.
+	if m.shouldPProf() {
+		f, err := os.Create(makePProfFilename(m.filebase, name, "cpuprof"))
+		if err != nil {
+			panic(err)
+		}
+		m.pprofFile = f
+		if err = pprof.StartCPUProfile(m.pprofFile); err != nil {
+			panic(err)
+		}
+	}
+	runtime.ReadMemStats(&m.curMark.startM)
+	m.curMark.startT = time.Now()
+}
+
+func (m *Metrics) closeMark() {
+	if m == nil || m.curMark == nil {
+		return
+	}
+	m.curMark.endT = time.Now()
+	if m.shouldPProf() {
+		pprof.StopCPUProfile()
+		m.pprofFile.Close()
+		m.pprofFile = nil
+	}
+	runtime.ReadMemStats(&m.curMark.endM)
+	if m.gc == GC {
+		runtime.GC()
+		runtime.ReadMemStats(&m.curMark.gcM)
+		if m.shouldPProf() {
+			// Collect a profile of the live heap. Do a
+			// second GC to force sweep completion so we
+			// get a complete snapshot of the live heap at
+			// the end of this phase.
+			runtime.GC()
+			f, err := os.Create(makePProfFilename(m.filebase, m.curMark.name, "memprof"))
+			if err != nil {
+				panic(err)
+			}
+			err = pprof.WriteHeapProfile(f)
+			if err != nil {
+				panic(err)
+			}
+			err = f.Close()
+			if err != nil {
+				panic(err)
+			}
+		}
+	}
+	m.marks = append(m.marks, m.curMark)
+	m.curMark = nil
+}
+
+// shouldPProf returns true if we should be doing pprof runs.
+func (m *Metrics) shouldPProf() bool {
+	return m != nil && len(m.filebase) > 0
+}
+
+// makeBenchString makes a benchmark string consumable by Go's benchmarking tools.
+func makeBenchString(name string) string {
+	needCap := true
+	ret := []rune("Benchmark")
+	for _, r := range name {
+		if unicode.IsSpace(r) {
+			needCap = true
+			continue
+		}
+		if needCap {
+			r = unicode.ToUpper(r)
+			needCap = false
+		}
+		ret = append(ret, r)
+	}
+	return string(ret)
+}
+
+func makePProfFilename(filebase, name, typ string) string {
+	return fmt.Sprintf("%s_%s.%s", filebase, makeBenchString(name), typ)
+}