Does sched_yield work?

Makefile

CFLAGS=-pthread
all: test

test.c

#include <pthread.h>
#include <sys/time.h>
#include <time.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/resource.h>

const int n_iter = 100;

static void work_hostname(void) {
	char buf[42];
	gethostname(buf, sizeof buf);
}

static void work_yield(void) {
	sched_yield();
}

static void * thread_start(void *arg) {
	void (*work)(void) = arg;
	struct timespec now;
	long long int end;
	clock_gettime(CLOCK_MONOTONIC, &now);

	end = now.tv_sec * 1000000000 + now.tv_nsec + 1000000000lu*10;

	while (1) {
		clock_gettime(CLOCK_MONOTONIC, &now);
		if (now.tv_sec * 1000000000 + now.tv_nsec > end) {
			break;
		}

		for (int i = 0; i < n_iter; i ++)
			work();
	}

	struct rusage usage;
	getrusage(RUSAGE_SELF, &usage);

	printf("%s: USER: %lld SYS: %lld CTXSW: %ld INVCTXSW: %ld\n",
		work == work_hostname ? "HOSTN" : "YIELD",
		usage.ru_utime.tv_sec * 1000000 + usage.ru_utime.tv_usec,
		usage.ru_stime.tv_sec * 1000000 + usage.ru_stime.tv_usec,
		usage.ru_nvcsw, usage.ru_nivcsw);


	return NULL;
}


int main() {
	pthread_attr_t attr;
	void *res;
	pthread_t thread_id[2];
	int ret;

	ret = pthread_attr_init(&attr);
	ret = pthread_attr_setstacksize(&attr, 4096);

	ret = pthread_create(&thread_id[0], &attr, thread_start, work_hostname);
	ret = pthread_create(&thread_id[1], &attr, thread_start, work_yield);


 	ret = pthread_attr_destroy(&attr);

	ret = pthread_join(thread_id[0], &res);
	ret = pthread_join(thread_id[1], &res);
}

yield_hostn.png

yield_hostn_user+sys.png