runtime: add Semacquire/Semrelease benchmarks

R=rsc
CC=golang-dev
https://golang.org/cl/4625065

src/pkg/runtime/sema_test.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 runtime_test
+
+import (
+	"runtime"
+	"sync/atomic"
+	"testing"
+)
+
+func BenchmarkSemaUncontended(b *testing.B) {
+	type PaddedSem struct {
+		sem uint32
+		pad [32]uint32
+	}
+	const CallsPerSched = 1000
+	procs := runtime.GOMAXPROCS(-1)
+	N := int32(b.N / CallsPerSched)
+	c := make(chan bool, procs)
+	for p := 0; p < procs; p++ {
+		go func() {
+			sem := new(PaddedSem)
+			for atomic.AddInt32(&N, -1) >= 0 {
+				runtime.Gosched()
+				for g := 0; g < CallsPerSched; g++ {
+					runtime.Semrelease(&sem.sem)
+					runtime.Semacquire(&sem.sem)
+				}
+			}
+			c <- true
+		}()
+	}
+	for p := 0; p < procs; p++ {
+		<-c
+	}
+}
+
+func benchmarkSema(b *testing.B, block, work bool) {
+	const CallsPerSched = 1000
+	const LocalWork = 100
+	procs := runtime.GOMAXPROCS(-1)
+	N := int32(b.N / CallsPerSched)
+	c := make(chan bool, procs)
+	c2 := make(chan bool, procs/2)
+	sem := uint32(0)
+	if block {
+		for p := 0; p < procs/2; p++ {
+			go func() {
+				runtime.Semacquire(&sem)
+				c2 <- true
+			}()
+		}
+	}
+	for p := 0; p < procs; p++ {
+		go func() {
+			foo := 0
+			for atomic.AddInt32(&N, -1) >= 0 {
+				runtime.Gosched()
+				for g := 0; g < CallsPerSched; g++ {
+					runtime.Semrelease(&sem)
+					if work {
+						for i := 0; i < LocalWork; i++ {
+							foo *= 2
+							foo /= 2
+						}
+					}
+					runtime.Semacquire(&sem)
+				}
+			}
+			c <- foo == 42
+			runtime.Semrelease(&sem)
+		}()
+	}
+	if block {
+		for p := 0; p < procs/2; p++ {
+			<-c2
+		}
+	}
+	for p := 0; p < procs; p++ {
+		<-c
+	}
+}
+
+func BenchmarkSemaSyntNonblock(b *testing.B) {
+	benchmarkSema(b, false, false)
+}
+
+func BenchmarkSemaSyntBlock(b *testing.B) {
+	benchmarkSema(b, true, false)
+}
+
+func BenchmarkSemaWorkNonblock(b *testing.B) {
+	benchmarkSema(b, false, true)
+}
+
+func BenchmarkSemaWorkBlock(b *testing.B) {
+	benchmarkSema(b, true, true)
+}