linux_clocks.c

/**
** Print time taken by various clocks


--- resolutions --- 

CLOCK_BOOTTIME           : 0.000000001
CLOCK_MONOTONIC          : 0.000000001
CLOCK_MONOTONIC_COARSE   : 0.003333333
CLOCK_MONOTONIC_RAW      : 0.000000001
CLOCK_REALTIME           : 0.000000001
CLOCK_REALTIME_COARSE    : 0.003333333


--- cpu time for 1000000000 calls ---

CLOCK_BOOTTIME           : 97.535666729
CLOCK_MONOTONIC          : 22.527615138
CLOCK_MONOTONIC_COARSE   : 7.233406602
CLOCK_MONOTONIC_RAW      : 92.978536610
CLOCK_REALTIME           : 22.894923621
CLOCK_REALTIME_COARSE    : 7.026963743

*/
#include <stdio.h>
#include <time.h>


void r(const char *name, int clk_id)
{
     struct timespec tp;
     clock_getres(clk_id, &tp);
     printf("%s: %ld.%.9ld\n", name,tp.tv_sec,tp.tv_nsec);
}


void timespec_diff(struct timespec *start, struct timespec *stop,
                   struct timespec *result)
{
    if ((stop->tv_nsec - start->tv_nsec) < 0) {
        result->tv_sec = stop->tv_sec - start->tv_sec - 1;
        result->tv_nsec = stop->tv_nsec - start->tv_nsec + 1000000000;
    } else {
        result->tv_sec = stop->tv_sec - start->tv_sec;
        result->tv_nsec = stop->tv_nsec - start->tv_nsec;
    }
}


void t(const char *name, int clk_id)
{
     struct timespec tp;
     clock_gettime(clk_id, &tp);
     printf("%s: %ld.%.9ld\n", name,tp.tv_sec,tp.tv_nsec);
}


void b(const char *name, int clk_id,long iter)
{
	 struct timespec start, stop,tp;
     clock_gettime(CLOCK_REALTIME, &start);
	 for( ; iter; iter--) {
		  clock_gettime(clk_id, &tp);		  
	 }
     clock_gettime(CLOCK_REALTIME, &stop);

	 timespec_diff(&start,&stop,&tp);
     printf("%s: %ld.%.9ld\n", name,tp.tv_sec,tp.tv_nsec);


}
int main(int argc, char **argv)
{

	 printf("\n\n--- resolutions --- \n\n");
     r("CLOCK_BOOTTIME           ",   CLOCK_BOOTTIME            );
     r("CLOCK_MONOTONIC          ",   CLOCK_MONOTONIC           );
     r("CLOCK_MONOTONIC_COARSE   ",   CLOCK_MONOTONIC_COARSE    );
     r("CLOCK_MONOTONIC_RAW      ",   CLOCK_MONOTONIC_RAW       );
     r("CLOCK_REALTIME           ",     CLOCK_REALTIME         );
     r("CLOCK_REALTIME_COARSE    ",   CLOCK_REALTIME_COARSE     );

	 long  n = 100L * 100L * 100L * 1000;
	 printf("\n\n--- cpu time for %ld calls ---\n\n", n);
     b("CLOCK_BOOTTIME           ",   CLOCK_BOOTTIME            ,n);
     b("CLOCK_MONOTONIC          ",   CLOCK_MONOTONIC           ,n);
     b("CLOCK_MONOTONIC_COARSE   ",   CLOCK_MONOTONIC_COARSE    ,n);
     b("CLOCK_MONOTONIC_RAW      ",   CLOCK_MONOTONIC_RAW       ,n);
     b("CLOCK_REALTIME           ",     CLOCK_REALTIME          ,n);
     b("CLOCK_REALTIME_COARSE    ",   CLOCK_REALTIME_COARSE     ,n);
	 
}