sched.c

#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
 
#define NLOOP_FOR_ESTIMATION 1000000000UL
#define NSECS_PER_MSEC 1000000UL
#define NSECS_PER_SEC 1000000000UL

static unsigned long nloop_per_msec;
static int total;
static struct timespec start;
struct timespec *logbuf;

static inline long diff_nsec(struct timespec before, struct timespec after)
{
        return ((after.tv_sec * NSECS_PER_SEC + after.tv_nsec)
                - (before.tv_sec * NSECS_PER_SEC + before.tv_nsec));
}

static unsigned long estimate_loops_per_msec()
{
        struct timespec before, after;
        clock_gettime(CLOCK_MONOTONIC, &before);
        unsigned long i;
        for (i = 0; i < NLOOP_FOR_ESTIMATION; i++)
		;
        clock_gettime(CLOCK_MONOTONIC, &after);
        return NLOOP_FOR_ESTIMATION * NSECS_PER_MSEC / diff_nsec(before, after);
}

static void child_fn(int id, struct timespec *buf)
{
        int i;
        for (i = 0; i < total; i++) {
                struct timespec now;
                unsigned long j;
                for (j = 0; j < nloop_per_msec; j++)
                        ;
                clock_gettime(CLOCK_MONOTONIC, &now);
                buf[i] = now;
        }
        for (i = 0; i < total; i++) {
                printf("%d\t%ld\t%d\n", id, diff_nsec(start, buf[i]) / NSECS_PER_MSEC, (i+1)*100/total);
        }
        exit(EXIT_SUCCESS);
}

int main(int argc, char *argv[])
{
        if (argc < 3) {
                fprintf(stderr, "usage: %s <nproc> <total[ms]>\n", argv[0]);
                exit(EXIT_FAILURE);
        }
        int nproc = atoi(argv[1]);
        total = atoi(argv[2]);
        if (nproc < 1) {
                fprintf(stderr, "<nproc>(%d) should be >= 1\n", nproc);
                exit(EXIT_FAILURE);
        }
        if (total < 1) {
                fprintf(stderr, "<total>(%d) should be >= 1\n", total);
                exit(EXIT_FAILURE);
        }

	puts("estimating the workload which takes just one milli-second...");
        nloop_per_msec = estimate_loops_per_msec();
	puts("end estimation");
	fflush(stdout);

        logbuf = malloc(total * sizeof(struct timespec));
	if (!logbuf)
		err(EXIT_FAILURE, "failed to allocate log buffer");

        clock_gettime(CLOCK_MONOTONIC, &start);
        int i;
        for (i = 0; i < nproc; i++) {
                pid_t pid = fork();
                if (pid < 0) {
			exit(EXIT_FAILURE);
                } else if (pid == 0) {
                        child_fn(i, logbuf);
			abort();
                }
        }
        for (i = 0; i < nproc; i++)
                wait(NULL);
        exit(EXIT_SUCCESS);
}