resolution of CLOCK_PROCESS_CPUTIME_ID

[Jan Stary]

Dear all,

the resolution of CLOCK_PROCESS_CPUTIME_ID,
as reported by clock_getres(), is 10000000 ns;
this seems to be the case on all archs I have.

This resolution seems to be coarser than
the actual cpu time reported (in a process that does nothing else),
such as 7233653 ns on this machine here.

FWIW, each of the OSes below (+Debian) returns 1 ns.

        Jan


#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <time.h>
#include <err.h>

void
show(clockid_t id, char* name)
{
        struct timespec ts;
        struct timespec cr;
        if (clock_gettime(id, &ts) == -1)
                err(1, NULL);
        if (clock_getres(id, &cr) == -1)
                err(1, NULL);
        printf("%s %10lld.%09ld s, %8ld ns resolution\n",
                name, ts.tv_sec, ts.tv_nsec, cr.tv_nsec);
}

int
main(void)
{
#ifdef  __APPLE__
        show(CLOCK_REALTIME,            "real time");
        show(CLOCK_MONOTONIC,           "monotonic");
        show(CLOCK_UPTIME_RAW,          "up time  ");
        show(CLOCK_PROCESS_CPUTIME_ID,  "proc time");
#elif __OpenBSD__
        show(CLOCK_REALTIME,            "real time");
        show(CLOCK_MONOTONIC,           "monotonic");
        show(CLOCK_BOOTTIME,            "boot time");
        show(CLOCK_UPTIME,              "up time  ");
        show(CLOCK_PROCESS_CPUTIME_ID,  "proc time");
#elif __FreeBSD__
        show(CLOCK_REALTIME,            "real time");
        show(CLOCK_MONOTONIC,           "monotonic");
        show(CLOCK_BOOTTIME,            "boot time");
        show(CLOCK_UPTIME,              "up time  ");
        show(CLOCK_PROCESS_CPUTIME_ID,  "proc time");
#elif __NetBSD__
        show(CLOCK_REALTIME,            "real time");
        show(CLOCK_MONOTONIC,           "monotonic");
        show(CLOCK_PROCESS_CPUTIME_ID,  "proc time");
#else
        show(CLOCK_REALTIME,            "real time");
        show(CLOCK_MONOTONIC,           "monotonic");
        show(CLOCK_BOOTTIME,            "boot time");
        show(CLOCK_PROCESS_CPUTIME_ID,  "proc time");
#endif
        return 0;
}