CASO - Bandwidth

/*
 * Fet per Sergi Granell
 * Compilar amb: gcc -Ofast -march=native bw.c -o bw
 * Usage: ./bw [dest file] [size]
 */

/*
 * No es recomana fer servir gettimeofday()
 * per mesurar temps: https://blog.habets.se/2010/09/gettimeofday-should-never-be-used-to-measure-time
 * Es recomana utilitzar clock_gettime(CLOCK_MONOTONIC, ...);
 * per mesurar intervals de temps en Linux i *BSD.
 */

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>

#define BLOCK_SIZE      (8 * 1024)
#define DEFAULT_FILE_SIZE   (500 * 1024 * 1024)
#define DEFAULT_FILE_NAME   "bwtest"

int main(int argc, const char *argv[])
{
    uint64_t diff;
    uint64_t size;
    uint64_t i;
    struct timespec start, end;
    double seconds;
    const char *file;
    int fd;
    void *buffer;

    if (argc > 1)
        file = argv[1];
    else
        file = DEFAULT_FILE_NAME;

    if (argc > 2)
        size = atoi(argv[2]);
    else
        size = DEFAULT_FILE_SIZE;

    printf("Target file: %s\n", file);
    printf("Target size: %dMB\n", size/(1024*1024));

    fd = open(file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if (fd < 0) {
        perror("Open error");
        goto err_open;
    }

    buffer = mmap(NULL, BLOCK_SIZE, PROT_READ | PROT_WRITE,
        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

    if (!buffer) {
        printf("Could not mmap %d bytes of memory.\n",
            BLOCK_SIZE);
        goto err_mmap;
    }

    /* Trigger page fault to have the pages available */
    memset(buffer, 0, BLOCK_SIZE);

    clock_gettime(CLOCK_MONOTONIC, &start);

    for (i = 0; i < size; i += BLOCK_SIZE) {
        write(fd, buffer, BLOCK_SIZE);
    }

    /* Flush data to disc */
    fsync(fd);

    clock_gettime(CLOCK_MONOTONIC, &end);

    close(fd);

    munmap(buffer, BLOCK_SIZE);

    diff = 1000000000L * (end.tv_sec - start.tv_sec) + end.tv_nsec - start.tv_nsec;
    seconds = diff/(double)1000000000L;

    printf("Elapsed time: %.9fs\n", seconds);
    printf("Bandwidth: %fMB/s\n", (size/(1024*1024))/seconds);

    return 0;

err_mmap:
    close(fd);
err_open:
    return -1;
}