internal/sysinfo: print cpu type from cpuinfo when internal cpu name is empty on Linux

Supports all linux operating systems. currently tested on x86, mips64le and loong64.

Example output:
$ go test -bench=.*
goos: linux
goarch: loong64
pkg: runtime
cpu: Loongson-3A5000-HV @ 2500.00MHz
BenchmarkSemTable/OneAddrCollision/n=1000         	   19261	     62302 ns/op
    ...

Change-Id: I02db12d70c11327e4625bb6e59f30dfaf37c2db0
Reviewed-on: https://go-review.googlesource.com/c/go/+/508735
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Bypass: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/internal/metadata/main.go

@@ -22,7 +22,7 @@ import (
 
 func main() {
 	fmt.Printf("# GOARCH: %s\n", runtime.GOARCH)
-	fmt.Printf("# CPU: %s\n", sysinfo.CPU.Name())
+	fmt.Printf("# CPU: %s\n", sysinfo.CPUName())
 
 	fmt.Printf("# GOOS: %s\n", runtime.GOOS)
 	ver, err := osinfo.Version()

src/go/build/deps_test.go

@@ -564,7 +564,7 @@ var depsRules = `
 	< net/rpc/jsonrpc;
 
 	# System Information
-	internal/cpu, sync
+	bufio, bytes, internal/cpu, io, os, strings, sync
 	< internal/sysinfo;
 
 	# Test-only

src/internal/sysinfo/cpuinfo_linux.go

@@ -0,0 +1,77 @@
+// Copyright 2023 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
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"os"
+	"strings"
+)
+
+func readLinuxProcCPUInfo(buf []byte) error {
+	f, err := os.Open("/proc/cpuinfo")
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = io.ReadFull(f, buf)
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return err
+	}
+
+	return nil
+}
+
+func osCpuInfoName() string {
+	modelName := ""
+	cpuMHz := ""
+
+	// The 512-byte buffer is enough to hold the contents of CPU0
+	buf := make([]byte, 512)
+	err := readLinuxProcCPUInfo(buf)
+	if err != nil {
+		return ""
+	}
+
+	scanner := bufio.NewScanner(bytes.NewReader(buf))
+	for scanner.Scan() {
+		line := scanner.Text()
+		if !strings.Contains(line, ":") {
+			continue
+		}
+
+		field := strings.SplitN(line, ": ", 2)
+		switch strings.TrimSpace(field[0]) {
+		case "Model Name", "model name":
+			modelName = field[1]
+		case "CPU MHz", "cpu MHz":
+			cpuMHz = field[1]
+		}
+	}
+
+	if modelName == "" {
+		return ""
+	}
+
+	if cpuMHz == "" {
+		return modelName
+	}
+
+	// The modelName field already contains the frequency information,
+	// so the cpuMHz field information is not needed.
+	// modelName filed example:
+	//	Intel(R) Core(TM) i7-10700 CPU @ 2.90GHz
+	f := [...]string{"GHz", "MHz"}
+	for _, v := range f {
+		if strings.Contains(modelName, v) {
+			return modelName
+		}
+	}
+
+	return modelName + " @ " + cpuMHz + "MHz"
+}

src/internal/sysinfo/cpuinfo_stub.go

@@ -0,0 +1,11 @@
+// Copyright 2023 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.
+
+//go:build !linux
+
+package sysinfo
+
+func osCpuInfoName() string {
+	return ""
+}

src/internal/sysinfo/sysinfo.go

@@ -7,25 +7,29 @@
 package sysinfo
 
 import (
-	internalcpu "internal/cpu"
+	"internal/cpu"
 	"sync"
 )
 
-type cpuInfo struct {
+var cpuInfo struct {
 	once sync.Once
 	name string
 }
 
-var CPU cpuInfo
-
-func (cpu *cpuInfo) Name() string {
-	cpu.once.Do(func() {
+func CPUName() string {
+	cpuInfo.once.Do(func() {
 		// Try to get the information from internal/cpu.
-		if name := internalcpu.Name(); name != "" {
-			cpu.name = name
+		if name := cpu.Name(); name != "" {
+			cpuInfo.name = name
 			return
 		}
+
 		// TODO(martisch): use /proc/cpuinfo and /sys/devices/system/cpu/ on Linux as fallback.
+		if name := osCpuInfoName(); name != "" {
+			cpuInfo.name = name
+			return
+		}
 	})
-	return cpu.name
+
+	return cpuInfo.name
 }

src/testing/benchmark.go

@@ -251,7 +251,7 @@ func (b *B) run() {
 		if b.importPath != "" {
 			fmt.Fprintf(b.w, "pkg: %s\n", b.importPath)
 		}
-		if cpu := sysinfo.CPU.Name(); cpu != "" {
+		if cpu := sysinfo.CPUName(); cpu != "" {
 			fmt.Fprintf(b.w, "cpu: %s\n", cpu)
 		}
 	})
@@ -668,7 +668,7 @@ 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 != "" {
+			if cpu := sysinfo.CPUName(); cpu != "" {
 				fmt.Printf("cpu: %s\n", cpu)
 			}
 		})