pipe atime benckmark

pipe_with_atime.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <pthread.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/unistd.h>

static int fds[2];
static pthread_t rp;

static void *rp_entry(void *arg) {
	char c[1];
	while (1 == read(fds[0], c, 1)) {
		if (*c == 'Q') break;
	}
	fprintf(stderr, "pipe read ok\n");
	return NULL;
}

int main(int argc, char *argv[]) {
	long i, n;
	int rc;
	if (argc < 2) {
		fprintf(stderr, "usage: pipe_test NNNNNN\n");
		return -1;
	}
	n = atol(argv[1]);
	pipe(fds);
	pthread_create(&rp, NULL, rp_entry, NULL);
	fprintf(stderr, "pipe write %ld...", n);
	for (i = 0; i < n; i++) {
		write(fds[1], "A", 1);
	}
	write(fds[1], "Q", 1);
	fprintf(stderr, "ok\n");
	pthread_join(rp, NULL);
	close(fds[0]);
	close(fds[1]);
	return 0;
}

pipe_without_atime.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <pthread.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/unistd.h>

static int fds[2];
static pthread_t rp;

static void *rp_entry(void *arg) {
	char c[1];
	while (1 == read(fds[0], c, 1)) {
		if (*c == 'Q') break;
	}
	fprintf(stderr, "pipe read ok\n");
	return NULL;
}

int main(int argc, char *argv[]) {
	long i, n;
	int rc;
	if (argc < 2) {
		fprintf(stderr, "usage: pipe_test NNNNNN\n");
		return -1;
	}
	n = atol(argv[1]);
	pipe(fds);
	//fcntl(fds[0], F_SETFL, O_NOATIME);
	pthread_create(&rp, NULL, rp_entry, NULL);
	fprintf(stderr, "pipe write %ld...", n);
	for (i = 0; i < n; i++) {
		write(fds[1], "A", 1);
	}
	write(fds[1], "Q", 1);
	fprintf(stderr, "ok\n");
	pthread_join(rp, NULL);
	close(fds[0]);
	close(fds[1]);
	return 0;
}

Profile with oprofile.
with atime:

2345      0.5745  vmlinux                  touch_atime
901       0.2208  vmlinux                  pipe_writev
233       0.0571  vmlinux                  pipe_readv

without atime

1001      0.1592  vmlinux                  pipe_readv
925       0.1471  vmlinux                  pipe_writev