sync()にどの程度かかるか計測用

sync_test.c

// Howto build
// $ gcc sync_test.c -lrt -lpthread -Wall
// rt for clock_gettime()
// pthread for pthread libraries
//
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <time.h>

#define DATA_SIZE (1024 * 1024)

static double *results;

static void show_result(int count)
{
  int i = 0;
	double average = 0.0f;
	double total = 0.0f;

	for (i = 0; i < count; i++) {
		total += results[i];
	//	printf("Writng 1MiB data took %5.5fs\n", results[i]);
	}

	average = total / (double) count;

	printf("Writing %d files average is %5.5fs\n", count, average);
}

static inline double get_msec(const struct timespec *st)
{
	return (double) st->tv_sec + (double) st->tv_nsec * 1e-9;
}

static void *start(void *arg)
{
	int fd = 0;
	char *buf = NULL;
	char name[256] =  { 0 };
	struct timespec start, end;
	long cnt = (long) arg;

	snprintf(name, sizeof(name) - 1, "./%010ld_test.bin", cnt);

	fd = open(name, O_CREAT | O_RDWR);
	assert(fd > 0);

	buf = malloc(DATA_SIZE);
	assert(buf != NULL);

	memset(buf, 0x0, DATA_SIZE);

	clock_gettime(CLOCK_REALTIME, &start);

	write(fd, buf, DATA_SIZE);
	sync();

	clock_gettime(CLOCK_REALTIME, &end);
	
	results[cnt] = get_msec(&end) - get_msec(&start);

	free(buf);
	close(fd);

	return NULL;
}

int main(int argc, char **argv)
{
	int count;
	pthread_t *threads;
	int ret;
	long i;

	if (argc != 2) {
		printf("usage: %s [number of threads]\n", argv[0]);
		exit(-1);
	}

	count = atoi(argv[1]);
	assert(count > 0);

	results = malloc(sizeof(double) * count);
	threads = malloc(sizeof(pthread_t) * count);
	for (i = 0; i < count; i++) {
		ret = pthread_create(&threads[i], NULL, &start, (void *) i);
		assert(ret == 0);
	}

	for (i = 0; i < count; i++) {
		ret = pthread_join(threads[i], NULL);
		assert(ret == 0);
	}
	
	show_result(count);

	free(results);
	free(threads);

	return 0;
}