Rust file I/O is very slow compared with C. Is something wrong?

Question

To compare file I/O performance between C and Rust, I write \"test\" to a file 100,000,000 times and read 4 bytes from a file 100,000,000 times.

Compared to C, the R

Answer 1

My Rust program was not using buffered IO. Thanks to BurntSushi5 and Andrew Henle's comments, the problem is solved.

$ strace ./rswrite
write(3, "test", 4)                     = 4
write(3, "test", 4)                     = 4
...
$ strace ./rswrite
read(3, "test", 4)                      = 4
read(3, "test", 4)                      = 4
...

I modified the code:

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();
    }
}

and

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();
    }
}

Now, I/O is buffered.

write(3, "testtesttesttesttesttesttesttest"..., 8192) = 8192
write(3, "testtesttesttesttesttesttesttest"..., 8192) = 8192
...

The performance is as fast as C.

$ time ./rswrite
real    0m1.341s
user    0m0.213s
sys     0m0.200s
$ time ./rsread_buf
real    0m0.596s
user    0m0.540s
sys     0m0.050s