random-syscall.c

/*
 * Copyright 2020 Matt Fleming
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

static inline unsigned long
clock_delta_now_secs(struct timespec *s)
{
	struct timespec now;

	clock_gettime(CLOCK_MONOTONIC_RAW, &now);
	return now.tv_sec - s->tv_sec;
}

static inline unsigned long
clock_delta_now_ns(struct timespec *s)
{
	struct timespec now;

	clock_gettime(CLOCK_MONOTONIC_RAW, &now);
	return now.tv_nsec - s->tv_nsec;
}

static inline void spin(unsigned long ns)
{
	struct timespec s;

	clock_gettime(CLOCK_MONOTONIC_RAW, &s);
	while (clock_delta_now_ns(&s) < ns)
		;
}

int main(int argc, char **argv)
{
	unsigned long duration, count;
	struct timespec start;

	if (argc < 2) {
		fprintf(stderr, "Usage: random-syscall <duration (secs)>\n");
		exit(1);
	}

	duration = strtoul(argv[1], NULL, 10);
	printf("Executing for %lu secs\n", duration);

	clock_gettime(CLOCK_MONOTONIC_RAW, &start);

	for (count = 0; clock_delta_now_secs(&start) < duration; count++) {
		struct timespec ns = {
			.tv_sec = 0,
			.tv_nsec = 10,
		};

		if (rand() % 2) {
			nanosleep(&ns, NULL);
		} else {
			spin(3000);
		}
	}

	printf("Loop count: %lu\n", count);

	return 0;
}