tsc_lol.c

/*
$ cc -O1 tsc_lol.c 
$ ./a.out 
1187.867 ms
11.879 ns per clock_gettime CLOCK_MONOTONIC
 */

#define _POSIX_C_SOURCE 199309L
#include <stdio.h>
#include <stdint.h>
#include <time.h>

static int64_t
timespec_diff(struct timespec a, struct timespec b)
{
	return (int64_t)(a.tv_sec - b.tv_sec) * 1000000000 + (int64_t)a.tv_nsec - (int64_t)b.tv_nsec;
}

int main(void) {
	int n = 100000000;
	struct timespec t0, t1;
	clock_gettime(CLOCK_MONOTONIC, &t0);

	for (int i = 0; i < n; i++) {
		struct timespec tmp;
		clock_gettime(CLOCK_MONOTONIC, &tmp);
	}

	clock_gettime(CLOCK_MONOTONIC, &t1);

	fprintf(stderr, "%.3f ms\n", (double)timespec_diff(t1, t0) / 1e6);
	fprintf(stderr, "%.3f ns per clock_gettime CLOCK_MONOTONIC\n", (double)timespec_diff(t1, t0) / n);

	return 0;
}