无法从 CPU 分析中获取数据

Question

我正在尝试学习使用 Go 的分析功能。考虑到这一点，我创建了这个简单的应用程序： https: //github.com/Matias-Barrios/countWords ，它只是计算给定txt文件 的单词出现次数。

问题是，创建.cpu.prof文件后我看不到任何内容。一旦我打开文件，我就会收到此错误：

(0) matias #> go tool pprof .cpu.prof 
File: main
Type: cpu
Time: Oct 9, 2019 at 12:38am (-03)
Duration: 201.31ms, Total samples = 0 No samples were found with the default sample value type.
Try "sample_index" command to analyze different sample values.
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 0, 0% of 0 total
      flat  flat%   sum%        cum   cum%
(pprof)

我在这里做错了什么？

注意：我的Go版本是go版本go1.13.1 linux/amd64

Answer 1

对我来说，问题是我的代码执行得太快。我所做的是使用runtime.SetCPUProfileRate更改采样率。请注意，在runtime.pprof.StartCPUProfile中，采样率为100 Hz，建议为500 Hz。func StartCPUProfile(w io.Writer) error {    // The runtime routines allow a variable profiling rate,    // but in practice operating systems cannot trigger signals    // at more than about 500 Hz, and our processing of the    // signal is not cheap (mostly getting the stack trace).    // 100 Hz is a reasonable choice: it is frequent enough to    // produce useful data, rare enough not to bog down the    // system, and a nice round number to make it easy to    // convert sample counts to seconds. Instead of requiring    // each client to specify the frequency, we hard code it.    const hz = 100    cpu.Lock()    defer cpu.Unlock()    if cpu.done == nil {         cpu.done = make(chan bool)    }    // Double-check.    if cpu.profiling {         return fmt.Errorf("cpu profiling already in use")     }    cpu.profiling = true    runtime.SetCPUProfileRate(hz)    go profileWriter(w)    return nil}但就我而言，将其设置为 500 Hz 还不够快。查看runtime.SetCPUProfileRate的代码后，您似乎可以提供高达100000 Hz的频率。将其设置为足够大的值后，它解决了我的问题。// SetCPUProfileRate sets the CPU profiling rate to hz samples per second.// If hz <= 0, SetCPUProfileRate turns off profiling.// If the profiler is on, the rate cannot be changed without first turning it off.//// Most clients should use the runtime/pprof package or// the testing package's -test.cpuprofile flag instead of calling// SetCPUProfileRate directly.func SetCPUProfileRate(hz int) {    // Clamp hz to something reasonable.    if hz < 0 {        hz = 0    }    if hz > 1000000 {        hz = 1000000    }    lock(&cpuprof.lock)    if hz > 0 {        if cpuprof.on || cpuprof.log != nil {            print("runtime: cannot set cpu profile rate until previous profile has finished.\n")            unlock(&cpuprof.lock)            return        }        cpuprof.on = true        cpuprof.log = newProfBuf(1, 1<<17, 1<<14)        hdr := [1]uint64{uint64(hz)}        cpuprof.log.write(nil, nanotime(), hdr[:], nil)        setcpuprofilerate(int32(hz))    } else if cpuprof.on {        setcpuprofilerate(0)        cpuprof.on = false        cpuprof.addExtra()        cpuprof.log.close()    }    unlock(&cpuprof.lock)}

Answer 2

Go 编程语言规范推迟陈述“defer”语句调用一个函数，该函数的执行被推迟到周围函数返回的那一刻，要么是因为周围函数执行了 return 语句，到达了其函数体的末尾，要么是因为相应的 goroutine 正在恐慌。修复CPU文件过早关闭的问题：func CPUprofiling() {    fd, err := os.Create(".cpu.prof")    if err != nil {        log.Fatalln(err.Error())    }    defer fd.Close()    pprof.StartCPUProfile(fd)    defer pprof.StopCPUProfile()}例如，package mainimport (    "bufio"    "flag"    "fmt"    "log"    "os"    "runtime/pprof"    "strings")var filename stringfunc main() {    cpu, err := os.Create(".cpu.prof")    if err != nil {        log.Fatalln(err.Error())    }    defer cpu.Close()    pprof.StartCPUProfile(cpu)    defer pprof.StopCPUProfile()    flag.StringVar(&filename, "f", "", "Path to the input file")    flag.Parse()    if filename == "" {        flag.Usage()        log.Fatalln()    }    for w, c := range getResults(filename) {        fmt.Printf("%-20s\t%d\n", w, c)    }    mem, err := os.Create(".mem.prof")    if err != nil {        log.Fatalln(err.Error())    }    defer mem.Close()    pprof.WriteHeapProfile(mem)}func getResults(path string) map[string]int {    results := make(map[string]int)    file, err := os.Open(filename)    defer file.Close()    if err != nil {        log.Fatalln(err.Error())    }    scanner := bufio.NewScanner(file)    scanner.Split(bufio.ScanWords)    for scanner.Scan() {        results[removeNonWordChars(scanner.Text())]++    }    delete(results, "")    return results}func removeNonWordChars(input string) string {    var result strings.Builder    result.Grow(len(input))    for _, r := range strings.ToLower(input) {        if r >= 'a' && r <= 'z' {            _, err := result.WriteRune(r)            if err != nil {                log.Fatalln(err.Error())            }        }    }    return result.String()}输出：$ go tool pprof .cpu.profFile: mainType: cpuTime: Oct 9, 2019 at 5:39am (EDT)Duration: 600.79ms, Total samples = 390ms (64.91%)Entering interactive mode (type "help" for commands, "o" for options)(pprof) topShowing nodes accounting for 320ms, 82.05% of 390ms totalShowing top 10 nodes out of 43      flat  flat%   sum%        cum   cum%     110ms 28.21% 28.21%      110ms 28.21%  syscall.Syscall      60ms 15.38% 43.59%       90ms 23.08%  runtime.mapassign_faststr      40ms 10.26% 53.85%       40ms 10.26%  unicode/utf8.DecodeRune      30ms  7.69% 61.54%       30ms  7.69%  strings.(*Builder).WriteRune      20ms  5.13% 66.67%       20ms  5.13%  runtime.slicebytetostring      20ms  5.13% 71.79%       20ms  5.13%  strings.ToLower      10ms  2.56% 74.36%       60ms 15.38%  bufio.ScanWords      10ms  2.56% 76.92%       10ms  2.56%  bufio.isSpace      10ms  2.56% 79.49%       10ms  2.56%  fmt.(*buffer).writeString      10ms  2.56% 82.05%       10ms  2.56%  memeqbody(pprof) quit$