rw-linux.c

#define _GNU_SOURCE

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <time.h>

double
getsec(void)
{
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return ts.tv_sec + ts.tv_nsec / 1000000000.0;
}


void test(int SZ)
{
    char data[SZ];

    double t0, t1;

    FILE *a = fopen("a.txt", "wb");
    fwrite(data, 1, SZ, a);
    fclose(a);

    int h = open("a.txt", O_RDWR);
    for (int i=0; i<4; i++) {
        int nloop = 4096;

        t0 = getsec();

        for (int li=0; li<nloop; li++) {
	    pread(h, data, SZ, 0);
        }

        t1 = getsec();

        printf("rd %f[usec]\n", ((t1-t0)/nloop)*1000000.0);
    }


    for (int i=0; i<4; i++) {
        int nloop = 4096;

        t0 = getsec();

        for (int li=0; li<nloop; li++) {
	    pwrite(h, data, SZ, 0);
        }

        t1 = getsec();

        printf("wr %f[usec]\n", ((t1-t0)/nloop)*1000000.0);
    }

    close(h);
}


int main()
{
    test(1);
    test(1024);
    test(1024*1024);
}