[英]Rust file I/O is very slow compared with C. Is something wrong?
為了比較C和Rust之間的文件I / O性能,我將“test”寫入100,000,000次文件並從文件中讀取4個字節100,000,000次。
與C相比,Rust代碼花費了超過450倍的系統時間用於寫入,140倍用於讀取。
我懷疑有更好的方法來實現快速I / O; 如何提高Rust中文件I / O的性能?
$ rustc --version
rustc 1.16.0
$ rustc rswrite.rs -C opt-level=3 # Rust for writing
$ time ./rswrite
real 1m8.411s
user 0m3.817s
sys 1m4.533s
$ rustc rsread.rs -C opt-level=3 # Rust for reading
$ time ./rsread
real 0m18.077s
user 0m2.130s
sys 0m15.910s
$ gcc -O3 cwrite.c -ocwrite # C for writing
$ time ./cwrite
real 0m1.564s
user 0m1.397s
sys 0m0.143s
$ gcc -O3 cread.c -ocread # C for reading
$ time ./cread
real 0m1.353s
user 0m1.240s
sys 0m0.113s
寫作的Rust代碼:
use std::fs;
use std::io::Write;
fn main() {
let b = b"test";
let mut f = fs::File::create("rs.dump").unwrap();
for _ in 0 .. 100_000_000 {
f.write(b).unwrap();
}
}
閱讀的Rust代碼:
use std::{fs, mem};
use std::io::Read;
fn main() {
let mut f = fs::File::open("rs.dump").unwrap();
let mut b: [u8; 4] = unsafe { mem::uninitialized() };
for _ in 0 .. 100_000_000 {
f.read_exact(&mut b).unwrap();
}
}
寫作的C代碼:
#include <stdio.h>
#define N 100000000
int main()
{
const char *teststr = "test";
FILE *fp = fopen("c.dump", "wb");
unsigned long long i;
for (i=0; i<N; i++) fwrite(teststr, 4, 1, fp);
fclose(fp);
return 0;
}
閱讀的C代碼:
#include <stdio.h>
#define N 100000000
int main() {
FILE *fp = fopen("c.dump", "rb");
long long i;
char buf[4];
for (i=0; i<N; i++) fread(buf, 4, 1, fp);
fclose(fp);
return 0;
}
我的Rust程序沒有使用緩沖IO。 感謝BurntSushi5和Andrew Henle的評論,問題解決了。
$ strace ./rswrite
write(3, "test", 4) = 4
write(3, "test", 4) = 4
...
$ strace ./rswrite
read(3, "test", 4) = 4
read(3, "test", 4) = 4
...
我修改了代碼:
use std::fs;
use std::io::{BufWriter, Write};
fn main() {
let b = b"test";
/**** Use std::io::BufWriter ****/
let mut f = BufWriter::new(fs::File::create("rs.dump").unwrap());
for _ in 0 .. 100_000_000 {
f.write(b).unwrap();
}
}
和
use std::{fs, mem};
use std::io::{BufReader, Read};
fn main() {
/**** Use std::io::BufReader ****/
let mut f = BufReader::new(fs::File::open("rs.dump").unwrap());
let mut b: [u8; 4] = unsafe { mem::uninitialized() };
for _ in 0 .. 100_000_000 {
f.read_exact(&mut b).unwrap();
}
}
現在,I / O被緩沖了。
write(3, "testtesttesttesttesttesttesttest"..., 8192) = 8192
write(3, "testtesttesttesttesttesttesttest"..., 8192) = 8192
...
性能和C一樣快。
$ time ./rswrite
real 0m1.341s
user 0m0.213s
sys 0m0.200s
$ time ./rsread_buf
real 0m0.596s
user 0m0.540s
sys 0m0.050s
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