math/randReadglobalRndlockedSourceGenerateFilerand.globalRnd.lk有两种方法可以提高性能。一种是在每个线程中使用独立的PRNG，另一种是预先生成写入数据。
这是一个尝试所有变体的示例程序。
package main
import (
"fmt"
"io/ioutil"
"log"
"math/rand"
"os"
"sort"
"sync"
"time"
)
var wg sync.WaitGroup
const N = 30
var elapsed_g [N]time.Duration
func SortAndLogElapsed(prefix string) {
sort.Slice(elapsed_g[:], func(i, j int) bool { return elapsed_g[i].Nanoseconds() < int64(elapsed_g[j].Nanoseconds()) })
for _, elapsed := range elapsed_g {
fmt.Println(prefix, elapsed)
}
}
func GenerateFile(start time.Time, id int) error {
defer wg.Done()
elapsed := time.Since(start)
buf := make([]byte, 7500000)
rand.Read(buf) // generate random data
randomFileName := fmt.Sprintf("/tmp/gotest-%v", rand.Int())
err := ioutil.WriteFile(randomFileName, buf, 0666)
if err != nil {
return err
}
defer os.Remove(randomFileName)
elapsed = time.Since(start)
// log.Printf("generate file %s done in %s", randomFileName, elapsed)
elapsed_g[id] = elapsed
return nil
}
func RunWithCommonPrng() {
start := time.Now()
for i := 0; i < N; i++ {
wg.Add(1)
go GenerateFile(start, i)
}
wg.Wait()
elapsed := time.Since(start)
SortAndLogElapsed("common PRNG: ")
log.Printf("done in %s", elapsed)
}
func GenerateFilePrivatePrng(id int, prng rand.Source, start time.Time) error {
defer wg.Done()
elapsed := time.Since(start)
buf := make([]byte, 7500000)
rand.New(prng).Read(buf) // generate random data
randomFileName := fmt.Sprintf("/tmp/gotest-%v", prng.Int63())
err := ioutil.WriteFile(randomFileName, buf, 0666)
if err != nil {
return err
}
defer os.Remove(randomFileName)
elapsed = time.Since(start)
elapsed_g[id] = elapsed
// log.Printf("generate file %s with private source: done in %s", randomFileName, elapsed)
return nil
}
func RunWithPrivatePrng() {
start := time.Now()
for i := 0; i < N; i++ {
wg.Add(1)
go GenerateFilePrivatePrng(i, rand.NewSource(int64(i)), start)
}
wg.Wait()
elapsed := time.Since(start)
SortAndLogElapsed("Private PRNG: ")
log.Printf("done in %s", elapsed)
}
func GenerateFileWithGivenData(id int, buf []byte, start time.Time) error {
defer wg.Done()
randomFileName := fmt.Sprintf("/tmp/gotest-%v", rand.Int())
err := ioutil.WriteFile(randomFileName, buf, 0666)
if err != nil {
return err
}
defer os.Remove(randomFileName)
elapsed := time.Since(start)
elapsed_g[id] = elapsed
// log.Printf("generate file %s with data: done in %s", randomFileName, elapsed)
return nil
}
func RunWithCommonData() {
buf := make([]byte, 7500000)
rand.Read(buf) // generate random data
start := time.Now()
for i := 0; i < N; i++ {
wg.Add(1)
go GenerateFileWithGivenData(i, buf, start)
}
wg.Wait()
elapsed := time.Since(start)
SortAndLogElapsed("Common data: ")
log.Printf("done in %s", elapsed)
}
func main() {
log.Printf("Used CPUs / Max CPUs: %d/%d", runtime.GOMAXPROCS(0), runtime.NumCPU())
RunWithCommonPrng()
RunWithPrivatePrng()
RunWithCommonData()
}
在 8 核 CPU 和 SSD 上的输出是这样的：
2022/10/02 00:00:08 Used CPUs / Max CPUs: 8/8
common PRNG: 9.943335ms
common PRNG: 15.12122ms
common PRNG: 20.856216ms
common PRNG: 26.636462ms
common PRNG: 32.041066ms
common PRNG: 37.450744ms
common PRNG: 43.286644ms
common PRNG: 48.695199ms
common PRNG: 54.518533ms
common PRNG: 59.858065ms
common PRNG: 65.620084ms
common PRNG: 71.111171ms
common PRNG: 76.388583ms
common PRNG: 81.609326ms
common PRNG: 87.465878ms
common PRNG: 92.623557ms
common PRNG: 98.35468ms
common PRNG: 103.606529ms
common PRNG: 109.28623ms
common PRNG: 114.981873ms
common PRNG: 120.26626ms
common PRNG: 125.530811ms
common PRNG: 131.222195ms
common PRNG: 136.399946ms
common PRNG: 142.305635ms
common PRNG: 147.687525ms
common PRNG: 153.002392ms
common PRNG: 158.769948ms
common PRNG: 164.241503ms
common PRNG: 169.531355ms
2022/10/02 00:00:08 done in 170.273377ms
Private PRNG: 16.255543ms
Private PRNG: 17.155624ms
Private PRNG: 17.477437ms
Private PRNG: 17.49527ms
Private PRNG: 17.521759ms
Private PRNG: 18.363554ms
Private PRNG: 19.800906ms
Private PRNG: 30.340522ms
Private PRNG: 31.551496ms
Private PRNG: 40.583626ms
Private PRNG: 54.682705ms
Private PRNG: 54.832006ms
Private PRNG: 54.983126ms
Private PRNG: 55.143073ms
Private PRNG: 56.517272ms
Private PRNG: 56.577967ms
Private PRNG: 57.718ms
Private PRNG: 58.770033ms
Private PRNG: 59.246808ms
Private PRNG: 59.608246ms
Private PRNG: 59.789123ms
Private PRNG: 60.028814ms
Private PRNG: 68.533662ms
Private PRNG: 69.606317ms
Private PRNG: 69.837988ms
Private PRNG: 71.488161ms
Private PRNG: 71.770842ms
Private PRNG: 72.036881ms
Private PRNG: 72.23509ms
Private PRNG: 73.037337ms
2022/10/02 00:00:08 done in 73.694825ms
Common data: 5.220506ms
Common data: 5.220523ms
Common data: 5.220524ms
Common data: 5.220526ms
Common data: 5.221125ms
Common data: 5.221169ms
Common data: 5.222472ms
Common data: 6.977304ms
Common data: 13.601358ms
Common data: 13.614532ms
Common data: 13.859067ms
Common data: 14.75378ms
Common data: 16.00253ms
Common data: 16.111086ms
Common data: 16.263291ms
Common data: 16.42076ms
Common data: 17.024946ms
Common data: 17.313631ms
Common data: 17.749351ms
Common data: 18.18497ms
Common data: 18.83511ms
Common data: 21.789867ms
Common data: 22.308659ms
Common data: 22.308701ms
Common data: 22.546815ms
Common data: 23.298865ms
Common data: 23.482138ms
Common data: 23.610855ms
Common data: 23.667347ms
Common data: 24.500486ms
2022/10/02 00:00:08 done in 25.205652ms
“公共数据”用于预生成的缓冲区。它表明 Golang 确实并行写入磁盘。它在线程之间分配 goroutines，这些 goroutines 占用 CPU 核心，直到 I/O 完成。
更新
这是打印 Linux 线程 ID 和 CPU 编号的代码。
package main
/*
#define _GNU_SOURCE
#include <sched.h>
*/
import "C"
import (
"fmt"
"io/ioutil"
"log"
"math/rand"
"os"
"runtime"
"sort"
"sync"
"syscall"
"time"
"github.com/pkg/profile"
)
func GetCpu() int {
var ret C.int = C.sched_getcpu()
return int(ret)
}
func GetThreadId() int {
return syscall.Gettid()
}
var wg sync.WaitGroup
const N = 30
var elapsed_g [N]time.Duration
func SortAndLogElapsed(prefix string) {
sort.Slice(elapsed_g[:], func(i, j int) bool { return elapsed_g[i].Nanoseconds() < int64(elapsed_g[j].Nanoseconds()) })
for _, elapsed := range elapsed_g {
fmt.Println(prefix, elapsed)
}
}
func GenerateFileWithGivenData(id int, buf []byte, start time.Time) error {
defer wg.Done()
randomFileName := fmt.Sprintf("/tmp/gotest-%v", rand.Int())
tid := GetThreadId()
cpu := GetCpu()
before := time.Now()
fmt.Printf("Before WriteFile:\t----\t%d\t%d\t%d\t%s\n", id, tid, cpu, before.String())
err := ioutil.WriteFile(randomFileName, buf, 0666)
after := time.Now()
tid = GetThreadId()
cpu = GetCpu()
fmt.Printf("After WriteFile:\t%d\t%d\t%d\t%d\t%s\n", after.Sub(before).Microseconds(), id, tid, cpu, after.String())
if err != nil {
return err
}
defer os.Remove(randomFileName)
elapsed := time.Since(start)
elapsed_g[id] = elapsed
// log.Printf("generate file %s with data: done in %s", randomFileName, elapsed)
return nil
}
func RunWithCommonData() {
buf := make([]byte, 7500000)
rand.Read(buf) // generate random data
fmt.Printf(" \tElapsed\tG\tTID\tCPU\ttime\n")
start := time.Now()
println("")
for i := 0; i < N; i++ {
wg.Add(1)
go GenerateFileWithGivenData(i, buf, start)
}
wg.Wait()
elapsed := time.Since(start)
SortAndLogElapsed("Common data: ")
log.Printf("done in %s", elapsed)
}
func main() {
log.Printf("Used CPUs / Max CPUs: %d/%d", runtime.GOMAXPROCS(0), runtime.NumCPU())
// RunWithCommonPrng()
// RunWithPrivatePrng()
defer profile.Start(profile.CPUProfile).Stop()
RunWithCommonData()
}
我系统的输出是（G internal goroutine ID, TID - Linux thread id, CPU - CPU number, last column is elapsed time）按时间排序：
Elapsed G TID CPU time
Before WriteFile: ---- 29 23379 0 2022-10-03 20:24:47.35247545 +0900 KST m=+0.006016977
Before WriteFile: ---- 0 23380 1 2022-10-03 20:24:47.352475589 +0900 KST m=+0.006017128
Before WriteFile: ---- 14 23383 7 2022-10-03 20:24:47.352506383 +0900 KST m=+0.006047950
Before WriteFile: ---- 7 23381 2 2022-10-03 20:24:47.352572666 +0900 KST m=+0.006114235
Before WriteFile: ---- 10 23377 6 2022-10-03 20:24:47.352634156 +0900 KST m=+0.006175692
Before WriteFile: ---- 8 23384 4 2022-10-03 20:24:47.352727575 +0900 KST m=+0.006269119
Before WriteFile: ---- 9 23385 5 2022-10-03 20:24:47.352766795 +0900 KST m=+0.006308348
After WriteFile: 4133 14 23383 7 2022-10-03 20:24:47.356640341 +0900 KST m=+0.010181880
After WriteFile: 4952 7 23381 2 2022-10-03 20:24:47.357525386 +0900 KST m=+0.011066917
After WriteFile: 5049 29 23379 0 2022-10-03 20:24:47.357525403 +0900 KST m=+0.011066934
After WriteFile: 4758 9 23385 5 2022-10-03 20:24:47.3575254 +0900 KST m=+0.011066928
After WriteFile: 4892 10 23377 6 2022-10-03 20:24:47.357526773 +0900 KST m=+0.011068303
After WriteFile: 5051 0 23380 1 2022-10-03 20:24:47.35752678 +0900 KST m=+0.011068311
After WriteFile: 4801 8 23384 4 2022-10-03 20:24:47.357529101 +0900 KST m=+0.011070629
Before WriteFile: ---- 12 23380 1 2022-10-03 20:24:47.357554923 +0900 KST m=+0.011096462
Before WriteFile: ---- 13 23377 6 2022-10-03 20:24:47.357555161 +0900 KST m=+0.011096695
Before WriteFile: ---- 1 23381 2 2022-10-03 20:24:47.357555163 +0900 KST m=+0.011096697
Before WriteFile: ---- 2 23381 2 2022-10-03 20:24:47.35756292 +0900 KST m=+0.011104452
Before WriteFile: ---- 11 23377 6 2022-10-03 20:24:47.3575642 +0900 KST m=+0.011105730
Before WriteFile: ---- 21 23385 5 2022-10-03 20:24:47.357570038 +0900 KST m=+0.011111568
Before WriteFile: ---- 25 23383 7 2022-10-03 20:24:47.357572217 +0900 KST m=+0.011113747
Before WriteFile: ---- 26 23379 0 2022-10-03 20:24:47.358768915 +0900 KST m=+0.012310542
Before WriteFile: ---- 27 23384 4 2022-10-03 20:24:47.361560776 +0900 KST m=+0.015102306
After WriteFile: 4020 25 23383 7 2022-10-03 20:24:47.361593063 +0900 KST m=+0.015134592
After WriteFile: 4873 12 23380 1 2022-10-03 20:24:47.362428015 +0900 KST m=+0.015969540
After WriteFile: 4858 21 23385 5 2022-10-03 20:24:47.362428103 +0900 KST m=+0.015969632
After WriteFile: 4865 2 23381 2 2022-10-03 20:24:47.362428238 +0900 KST m=+0.015969769
After WriteFile: 4864 11 23377 6 2022-10-03 20:24:47.362428347 +0900 KST m=+0.015969877
Before WriteFile: ---- 15 23385 5 2022-10-03 20:24:47.362454039 +0900 KST m=+0.015995570
Before WriteFile: ---- 28 23380 1 2022-10-03 20:24:47.362454041 +0900 KST m=+0.015995573
Before WriteFile: ---- 23 23377 6 2022-10-03 20:24:47.362454121 +0900 KST m=+0.015995651
Before WriteFile: ---- 16 23385 5 2022-10-03 20:24:47.362462845 +0900 KST m=+0.016004374
Before WriteFile: ---- 22 23377 6 2022-10-03 20:24:47.362479715 +0900 KST m=+0.016021242
After WriteFile: 4902 26 23379 0 2022-10-03 20:24:47.363671623 +0900 KST m=+0.017213150
Before WriteFile: ---- 18 23386 6 2022-10-03 20:24:47.365182522 +0900 KST m=+0.018724057
After WriteFile: 8764 13 23383 7 2022-10-03 20:24:47.366320071 +0900 KST m=+0.019861611
Before WriteFile: ---- 17 23379 0 2022-10-03 20:24:47.366374805 +0900 KST m=+0.019916338
After WriteFile: 4902 27 23384 4 2022-10-03 20:24:47.366463028 +0900 KST m=+0.020004556
After WriteFile: 4729 28 23380 1 2022-10-03 20:24:47.367183315 +0900 KST m=+0.020724852
After WriteFile: 4720 16 23385 5 2022-10-03 20:24:47.367183317 +0900 KST m=+0.020724850
Before WriteFile: ---- 19 23385 5 2022-10-03 20:24:47.367230069 +0900 KST m=+0.020771602
Before WriteFile: ---- 20 23384 4 2022-10-03 20:24:47.367748633 +0900 KST m=+0.021290163
Before WriteFile: ---- 3 23391 3 2022-10-03 20:24:47.368046383 +0900 KST m=+0.021587923
Before WriteFile: ---- 5 23388 1 2022-10-03 20:24:47.36857915 +0900 KST m=+0.022120682
Before WriteFile: ---- 4 23380 1 2022-10-03 20:24:47.368590097 +0900 KST m=+0.022131628
Before WriteFile: ---- 6 23393 2 2022-10-03 20:24:47.370493582 +0900 KST m=+0.024035118
After WriteFile: 10260 22 23377 6 2022-10-03 20:24:47.372740578 +0900 KST m=+0.026282112
After WriteFile: 5326 20 23384 4 2022-10-03 20:24:47.37307519 +0900 KST m=+0.026616720
After WriteFile: 10922 23 23387 0 2022-10-03 20:24:47.373376163 +0900 KST m=+0.026917695
After WriteFile: 5613 3 23391 3 2022-10-03 20:24:47.373660058 +0900 KST m=+0.027201605
After WriteFile: 5332 4 23380 1 2022-10-03 20:24:47.373922339 +0900 KST m=+0.027463865
After WriteFile: 8871 18 23377 6 2022-10-03 20:24:47.374053982 +0900 KST m=+0.027595513
After WriteFile: 7880 17 23384 4 2022-10-03 20:24:47.374255159 +0900 KST m=+0.027796694
After WriteFile: 12127 15 23387 0 2022-10-03 20:24:47.37458126 +0900 KST m=+0.028122790
After WriteFile: 7422 19 23391 3 2022-10-03 20:24:47.374652483 +0900 KST m=+0.028194020
Before WriteFile: ---- 24 23377 6 2022-10-03 20:24:47.375338247 +0900 KST m=+0.028879777
After WriteFile: 5111 6 23393 2 2022-10-03 20:24:47.375605341 +0900 KST m=+0.029146871
After WriteFile: 19459 1 23392 5 2022-10-03 20:24:47.377014458 +0900 KST m=+0.030555986
After WriteFile: 3847 24 23377 6 2022-10-03 20:24:47.379185393 +0900 KST m=+0.032726920
After WriteFile: 10778 5 23388 0 2022-10-03 20:24:47.379358058 +0900 KST m=+0.032899584
它表明 goroutines 在我的 8 核 CPU 的所有内核上的许多不同线程中运行。看起来最快的 IO 是在那些保留了线程和 CPU 的 goroutine 中。而且似乎停放/取消停放线程会使阻塞 IO 变慢。
我用 100 个 goroutines 运行相同的代码。最坏的情况有 60 毫秒那么大，但它不是最后一个，中间的一个。即使在最后，也有 5.5 毫秒的快速写入。