testing: print cpu type as label for benchmarks

Supports 386 and amd64 architectures on all operating systems.

Example output:
$ go test -bench=.*
goos: darwin
goarch: amd64
pkg: strconv
cpu: Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz
BenchmarkAtof64Decimal-4        	24431032	        46.8 ns/op
...

As the displayed CPU information is only used for information
purposes it is lazily initialized when needed using the new
internal/sysinfo package.

This allows internal/cpu to stay without dependencies and avoid
initialization costs when the CPU information is not needed as
the new code to query the CPU name in internal/cpu can be
dead code eliminated if not used.

Fixes #39214

Change-Id: I77ae5c5d2fed6b28fa78dd45075f9f0a6a7f1bfd
Reviewed-on: https://go-review.googlesource.com/c/go/+/263804
Trust: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/go/build/deps_test.go

@@ -467,6 +467,10 @@ var depsRules = `
 	< net/rpc
 	< net/rpc/jsonrpc;
 
+	# System Information
+	internal/cpu, sync
+	< internal/sysinfo;
+
 	# Test-only
 	log
 	< testing/iotest
@@ -475,7 +479,7 @@ var depsRules = `
 	FMT, flag, math/rand
 	< testing/quick;
 
-	FMT, flag, runtime/debug, runtime/trace
+	FMT, flag, runtime/debug, runtime/trace, internal/sysinfo
 	< testing;
 
 	internal/testlog, runtime/pprof, regexp

src/internal/cpu/cpu_no_name.go

@@ -0,0 +1,19 @@
+// 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.
+
+// +build !386
+// +build !amd64
+
+package cpu
+
+// Name returns the CPU name given by the vendor
+// if it can be read directly from memory or by CPU instructions.
+// If the CPU name can not be determined an empty string is returned.
+//
+// Implementations that use the Operating System (e.g. sysctl or /sys/)
+// to gather CPU information for display should be placed in internal/sysinfo.
+func Name() string {
+	// "A CPU has no name".
+	return ""
+}

src/internal/cpu/cpu_x86.go

@@ -38,6 +38,8 @@ const (
 	cpuid_ADX  = 1 << 19
 )
 
+var maxExtendedFunctionInformation uint32
+
 func doinit() {
 	options = []option{
 		{Name: "adx", Feature: &X86.HasADX},
@@ -65,6 +67,8 @@ func doinit() {
 		return
 	}
 
+	maxExtendedFunctionInformation, _, _, _ = cpuid(0x80000000, 0)
+
 	_, _, ecx1, edx1 := cpuid(1, 0)
 	X86.HasSSE2 = isSet(edx1, cpuid_SSE2)
 
@@ -103,3 +107,48 @@ func doinit() {
 func isSet(hwc uint32, value uint32) bool {
 	return hwc&value != 0
 }
+
+// Name returns the CPU name given by the vendor.
+// If the CPU name can not be determined an
+// empty string is returned.
+func Name() string {
+	if maxExtendedFunctionInformation < 0x80000004 {
+		return ""
+	}
+
+	data := make([]byte, 0, 3*4*4)
+
+	var eax, ebx, ecx, edx uint32
+	eax, ebx, ecx, edx = cpuid(0x80000002, 0)
+	data = appendBytes(data, eax, ebx, ecx, edx)
+	eax, ebx, ecx, edx = cpuid(0x80000003, 0)
+	data = appendBytes(data, eax, ebx, ecx, edx)
+	eax, ebx, ecx, edx = cpuid(0x80000004, 0)
+	data = appendBytes(data, eax, ebx, ecx, edx)
+
+	// Trim leading spaces.
+	for len(data) > 0 && data[0] == ' ' {
+		data = data[1:]
+	}
+
+	// Trim tail after and including the first null byte.
+	for i, c := range data {
+		if c == '\x00' {
+			data = data[:i]
+			break
+		}
+	}
+
+	return string(data)
+}
+
+func appendBytes(b []byte, args ...uint32) []byte {
+	for _, arg := range args {
+		b = append(b,
+			byte((arg >> 0)),
+			byte((arg >> 8)),
+			byte((arg >> 16)),
+			byte((arg >> 24)))
+	}
+	return b
+}

src/internal/sysinfo/sysinfo.go

@@ -0,0 +1,31 @@
+// 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 sysinfo implements high level hardware information gathering
+// that can be used for debugging or information purposes.
+package sysinfo
+
+import (
+	internalcpu "internal/cpu"
+	"sync"
+)
+
+type cpuInfo struct {
+	once sync.Once
+	name string
+}
+
+var CPU cpuInfo
+
+func (cpu *cpuInfo) Name() string {
+	cpu.once.Do(func() {
+		// Try to get the information from internal/cpu.
+		if name := internalcpu.Name(); name != "" {
+			cpu.name = name
+			return
+		}
+		// TODO(martisch): use /proc/cpuinfo and /sys/devices/system/cpu/ on Linux as fallback.
+	})
+	return cpu.name
+}

src/testing/benchmark.go

@@ -8,6 +8,7 @@ import (
 	"flag"
 	"fmt"
 	"internal/race"
+	"internal/sysinfo"
 	"io"
 	"math"
 	"os"
@@ -262,6 +263,9 @@ func (b *B) run() {
 		if b.importPath != "" {
 			fmt.Fprintf(b.w, "pkg: %s\n", b.importPath)
 		}
+		if cpu := sysinfo.CPU.Name(); cpu != "" {
+			fmt.Fprintf(b.w, "cpu: %s\n", cpu)
+		}
 	})
 	if b.context != nil {
 		// Running go test --test.bench
@@ -648,6 +652,9 @@ func (b *B) Run(name string, f func(b *B)) bool {
 			if b.importPath != "" {
 				fmt.Printf("pkg: %s\n", b.importPath)
 			}
+			if cpu := sysinfo.CPU.Name(); cpu != "" {
+				fmt.Printf("cpu: %s\n", cpu)
+			}
 		})
 
 		fmt.Println(benchName)