net: add TCP benchmarks

Current results on linux_amd64, 8 HT cores @2.4GHz:
BenchmarkTCPOneShot	   10000	    194037 ns/op
BenchmarkTCPOneShot-2	   20000	     93641 ns/op
BenchmarkTCPOneShot-4	   20000	     94039 ns/op
BenchmarkTCPOneShot-8	   20000	     94667 ns/op
BenchmarkTCPOneShot-16	   10000	    301924 ns/op
BenchmarkTCPOneShotTimeout	   10000	    193264 ns/op
BenchmarkTCPOneShotTimeout-2	   20000	     98247 ns/op
BenchmarkTCPOneShotTimeout-4	   20000	     94442 ns/op
BenchmarkTCPOneShotTimeout-8	   20000	     95297 ns/op
BenchmarkTCPOneShotTimeout-16	   10000	    307970 ns/op
BenchmarkTCPPersistent	   50000	     52050 ns/op
BenchmarkTCPPersistent-2	  100000	     29452 ns/op
BenchmarkTCPPersistent-4	  100000	     28823 ns/op
BenchmarkTCPPersistent-8	   50000	     30473 ns/op
BenchmarkTCPPersistent-16	   10000	    311777 ns/op
BenchmarkTCPPersistentTimeout	   50000	     32574 ns/op
BenchmarkTCPPersistentTimeout-2	   50000	     29723 ns/op
BenchmarkTCPPersistentTimeout-4	  100000	     28592 ns/op
BenchmarkTCPPersistentTimeout-8	  100000	     28997 ns/op
BenchmarkTCPPersistentTimeout-16	   10000	    314354 ns/op

R=golang-dev, alex.brainman, dave, mikioh.mikioh, r, iant, bradfitz, iant
CC=golang-dev
https://golang.org/cl/6458128

src/pkg/net/tcp_test.go

+// Copyright 2012 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 net
+
+import (
+	"runtime"
+	"testing"
+	"time"
+)
+
+func BenchmarkTCPOneShot(b *testing.B) {
+	benchmarkTCP(b, false, false)
+}
+
+func BenchmarkTCPOneShotTimeout(b *testing.B) {
+	benchmarkTCP(b, false, true)
+}
+
+func BenchmarkTCPPersistent(b *testing.B) {
+	benchmarkTCP(b, true, false)
+}
+
+func BenchmarkTCPPersistentTimeout(b *testing.B) {
+	benchmarkTCP(b, true, true)
+}
+
+func benchmarkTCP(b *testing.B, persistent, timeout bool) {
+	const msgLen = 512
+	conns := b.N
+	numConcurrent := runtime.GOMAXPROCS(-1) * 16
+	msgs := 1
+	if persistent {
+		conns = numConcurrent
+		msgs = b.N / conns
+		if msgs == 0 {
+			msgs = 1
+		}
+		if conns > b.N {
+			conns = b.N
+		}
+	}
+	sendMsg := func(c Conn, buf []byte) bool {
+		n, err := c.Write(buf)
+		if n != len(buf) || err != nil {
+			b.Logf("Write failed: %v", err)
+			return false
+		}
+		return true
+	}
+	recvMsg := func(c Conn, buf []byte) bool {
+		for read := 0; read != len(buf); {
+			n, err := c.Read(buf)
+			read += n
+			if err != nil {
+				b.Logf("Read failed: %v", err)
+				return false
+			}
+		}
+		return true
+	}
+	ln, err := Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		b.Fatalf("Listen failed: %v", err)
+	}
+	defer ln.Close()
+	// Acceptor.
+	go func() {
+		for {
+			c, err := ln.Accept()
+			if err != nil {
+				break
+			}
+			// Server connection.
+			go func(c Conn) {
+				defer c.Close()
+				if timeout {
+					c.SetDeadline(time.Now().Add(time.Hour)) // Not intended to fire.
+				}
+				var buf [msgLen]byte
+				for m := 0; m < msgs; m++ {
+					if !recvMsg(c, buf[:]) || !sendMsg(c, buf[:]) {
+						break
+					}
+				}
+			}(c)
+		}
+	}()
+	sem := make(chan bool, numConcurrent)
+	for i := 0; i < conns; i++ {
+		sem <- true
+		// Client connection.
+		go func() {
+			defer func() {
+				<-sem
+			}()
+			c, err := Dial("tcp", ln.Addr().String())
+			if err != nil {
+				b.Logf("Dial failed: %v", err)
+				return
+			}
+			defer c.Close()
+			if timeout {
+				c.SetDeadline(time.Now().Add(time.Hour)) // Not intended to fire.
+			}
+			var buf [msgLen]byte
+			for m := 0; m < msgs; m++ {
+				if !sendMsg(c, buf[:]) || !recvMsg(c, buf[:]) {
+					break
+				}
+			}
+		}()
+	}
+	for i := 0; i < cap(sem); i++ {
+		sem <- true
+	}
+}