2017-12-18 427 views
6

在以下代碼中,我使用golang中的bufio將消息寫入文件。我的磁盤I/O速度約爲1000M/s。奇怪的是,當寫入文件的大小小於20G時,寫入速度大約爲800M〜900M每秒,比I/O速度略低一點。但是,當文件大小超過21G時,我發現寫入速度大約爲每秒200M,遠遠低於I/O速度。我不知道爲什麼,有人可以幫助我?謝謝。golang的磁盤寫入性能

package main 

import "fmt" 
import (
    "os" 
    "time" 
    "flag" 
    "bufio" 
) 

func main() { 
    var pRound = flag.Int64("round", 3500000, "loop round") 
    flag.Parse() 

    var message string 
    for i := 0; i < 1024; i++ { 
     message += "1234567890" 
    } 
    message += "\n" 

    f, err := os.OpenFile("server", os.O_CREATE|os.O_APPEND|os.O_RDWR, 0666) 
    if err != nil { 
     fmt.Println(err) 
     return 
    } 
    w := bufio.NewWriter(f) 

    var i int64 = 0 
    round := *pRound 
    start := time.Now() 
    for i = 0; i < round; i++ { 
     w.WriteString(message) 
    } 
    w.Flush() 
    f.Close() 
    end := time.Now() 

    nanoseconds := end.Sub(start).Nanoseconds() 
    speed := 1000000000 * round/nanoseconds 

    fmt.Printf("round: %v\n", round) 
    fmt.Printf("Nanoseconds: %v\n", nanoseconds) 
    fmt.Printf("speed: %v\n", speed) 
} 

我想我已經問過一個愚蠢的問題。關於Vorsprung的迴應,我在這裏展示了我的C代碼。我用C語言再次測試它。我用go語言找到了相同的結果。我的測試結果是:

./a.out 10000 
seconds: 7 
milliseconds: 260910 
total: 10485760000 Bytes 
total: 10000 M 
total: 9.76562 G 
speed: 1377.24 M/s 


./a.out 20000 
seconds: 24 
milliseconds: 7249 
total: 20971520000 Bytes 
total: 20000 M 
total: 19.5312 G 
speed: 833.082 M/s 


./a.out 30000 
seconds: 80 
milliseconds: 518970 
total: 31457280000 Bytes 
total: 30000 M 
total: 29.2969 G 
speed: 372.583 M/s 



./a.out 40000 
seconds: 134 
milliseconds: 615910 
total: 41943040000 Bytes 
total: 40000 M 
total: 39.0625 G 
speed: 297.142 M/s 

以下是我的C代碼:

#include <fcntl.h> 
#include <errno.h> 
#include <limits.h> 
#include <sys/uio.h> 
#include <time.h> 
#include <sys/time.h> 
#include <iostream> 
#include <string.h> 
#include <stdlib.h> 

int main(int argc, char* argv[]) { 
    if (argc != 2) { 
    std::cout << "usage: " << argv[0] << " round" << std::endl; 
    return -1; 
    } 
    int round = atoi(argv[1]); 

    int fd = open("file.data", O_CREAT | O_APPEND | O_RDWR, 0666); 
    if (fd == -1) { 
    std::cout << "open file error: " << strerror(errno) << std::endl; 
    return -1; 
    } 

    struct iovec vec[IOV_MAX]; 
    int len = 1024; 
    for (int i = 0; i < IOV_MAX; i++) { 
    vec[i].iov_base = new char[len]; 
    vec[i].iov_len = len; 

    char *buf = NULL; 
    for (int j = 0; j < len - 1; j++) { 
     buf = (char*)vec[i].iov_base; 
     buf[j] = j % 10 + '1'; 
    } 
    buf[len - 1] = '\n'; 
    } 

    timeval tv1; 
    gettimeofday(&tv1, NULL); 
    for (int i = 0; i < round; i++) { 
    writev(fd, vec, IOV_MAX); 
    } 

    close(fd); 

    timeval tv2; 
    gettimeofday(&tv2, NULL); 

    for (int i = 0; i < IOV_MAX; i++) { 
    char* buf = (char*)vec[i].iov_base; 
    delete[] buf; 
    } 

    std::cout << "seconds: " << tv2.tv_sec - tv1.tv_sec << std::endl; 
    std::cout << "milliseconds: " << tv2.tv_usec - tv1.tv_usec << std::endl; 
    int64_t total = int64_t(len) * IOV_MAX * round; 
    float t = (tv2.tv_sec - tv1.tv_sec) * 1000000.0 + (tv2.tv_usec - tv1.tv_usec); 
    float speed = 1000000.0 * total/t/1024/1024; 
    std::cout << "total: " << total << " Bytes" << std::endl; 
    std::cout << "total: " << total/1024.0/1024.0 << " M" << std::endl; 
    std::cout << "total: " << total/1024.0/1024.0/1024.0 << " G" << std::endl; 
    std::cout << "speed: " << speed << " M/s" << std::endl; 
    return 0; 
} 

現在我diskio.go測試結果顯示在這裏。因爲我不知道如何評論簡單閱讀的結果,所以我在這裏展示它。

time ./diskio -size=4 
written: 4294967296B 26237051975ns 4.29GB 26.24s 163.70MB/s 
real 0m26.980s 
user 0m0.397s 
sys  0m4.874s 


time ./diskio -size=8 
written: 8589934592B 57803019028ns 8.59GB 57.80s 148.61MB/s 
real 0m59.192s 
user 0m0.813s 
sys  0m9.607s 



time ./diskio -size=10 
written: 10737418240B 68331989999ns 10.74GB 68.33s 157.14MB/s 
real 1m10.288s 
user 0m0.946s 
sys  0m12.024s 




time ./diskio -size=20 
written: 21474836480B 141169506440ns 21.47GB 141.17s 152.12MB/s 
real 2m25.037s 
user 0m1.881s 
sys  0m24.029s 


time ./diskio -size=30 
written: 32212254720B 203807569664ns 32.21GB 203.81s 158.05MB/s 
real 3m29.345s 
user 0m2.925s 
sys  0m33.528s 

diskio.go來自https://stackoverflow.com/a/47889346/5616809

我覺得我得到了答案,測試結果由磁盤緩衝區的原因造成的。我測試了我的硬盤速度使用hdparm表彰,而我得到這個:

hdparm -Tt /dev/sde1 
/dev/sde1: 
Timing cached reads: 18166 MB in 2.00 seconds = 9093.93 MB/sec 
Timing buffered disk reads: 584 MB in 3.01 seconds = 194.18 MB/sec 

所以,也許我的程序書面方式字節緩衝區時,文件大小小於約18166M。之後,該程序正在寫入磁盤,所以速度較慢。

+0

很可能是因爲你的磁盤緩衝區在那一點飽和了嗎? – Flimzy

+0

幾個月前,我用C語言中的'writev'方法寫了一個類似的過程。我發現寫入速度幾乎等於磁盤I/O速度。這是否可以證明它與磁盤緩衝區無關? –

+0

剖析你的代碼,這是關於你最好的希望。如果性能下降超過21G,則應該在配置文件中看到一些內容。最有可能的是等待。 – Marc

回答

0

我覺得我得到的回答這個問題。由於我的磁盤I/O速度約爲194M/s,磁盤緩衝I/O約爲9093M/s。但磁盤緩衝區大小約爲18166M。所以當文件大小小於20G時寫入速度會更快。我用這個命令來測試我的磁盤I/O速度:

hdparm -Tt /dev/sde1 
/dev/sde1: 
Timing cached reads: 18166 MB in 2.00 seconds = 9093.93 MB/sec 
Timing buffered disk reads: 584 MB in 3.01 seconds = 194.18 MB/sec 
3

您的問題是無法重複的。你的代碼有錯誤。

我們預計磁盤寫入時間會受到很多因素的影響:程序,其他程序,操作系統,硬件等等。

啓動獨立的專用機器並運行diskio.go程序。你會得到什麼結果?例如,我的機器上:

$ go build diskio.go 
$ time ./diskio -size=32 
written: 34359738368B 154333936544ns 34.36GB 154.33s 222.63MB/s 
real 2m35.323s 
user 0m6.418s 
sys  0m41.994s 
$ time ./diskio -size=16 
written: 17179869184B 77901269159ns 17.18GB 77.90s 220.53MB/s 
real 1m18.746s 
user 0m2.849s 
sys  0m21.721s 
$ time ./diskio -size=8 
written: 8589934592B 38940248134ns 8.59GB 38.94s 220.59MB/s 
real 0m39.625s 
user 0m1.719s 
sys  0m12.493s 
$ time ./diskio -size=1 
written: 1073741824B 4738082404ns 1.07GB 4.74s 226.62MB/s 
real 0m4.851s 
user 0m0.069s 
sys  0m0.755s 
$ 

正如預期的那樣,很少有時間在節目中度過,更多的時間是在操作系統中度過的,大量的時間都花在等待在磁盤上。寫入速度沒有急劇變化。

diskio.go

package main 

import (
    "bufio" 
    "flag" 
    "fmt" 
    "os" 
    "time" 
) 

func writeFile(fSize int64) error { 
    fName := `/home/peter/diskio` // test file 
    defer os.Remove(fName) 
    f, err := os.Create(fName) 
    if err != nil { 
     return err 
    } 
    const defaultBufSize = 4096 
    buf := make([]byte, defaultBufSize) 
    buf[len(buf)-1] = '\n' 
    w := bufio.NewWriterSize(f, len(buf)) 

    start := time.Now() 
    written := int64(0) 
    for i := int64(0); i < fSize; i += int64(len(buf)) { 
     nn, err := w.Write(buf) 
     written += int64(nn) 
     if err != nil { 
      return err 
     } 
    } 
    err = w.Flush() 
    if err != nil { 
     return err 
    } 
    err = f.Sync() 
    if err != nil { 
     return err 
    } 
    since := time.Since(start) 

    err = f.Close() 
    if err != nil { 
     return err 
    } 
    fmt.Printf("written: %dB %dns %.2fGB %.2fs %.2fMB/s\n", 
     written, since, 
     float64(written)/1000000000, float64(since)/float64(time.Second), 
     (float64(written)/1000000)/(float64(since)/float64(time.Second)), 
    ) 
    return nil 
} 

var size = flag.Int("size", 8, "file size in GiB") 

func main() { 
    flag.Parse() 
    fSize := int64(*size) * (1024 * 1024 * 1024) 
    err := writeFile(fSize) 
    if err != nil { 
     fmt.Fprintln(os.Stderr, fSize, err) 
    } 
} 

遊樂場:https://play.golang.org/p/vnjnpgMzsV

+0

我試着在這裏評論代碼,但我不知道如何。所以我再次將我的測試結果上傳到我的問題中。我想我的速度測試出了問題。謝謝。 –

+0

謝謝。我想我已經得到了答案。 –