How precise is busy sleeping on nic clock ?
Posted by Anonymous on Tue 2nd Nov 2021 11:56
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/*
# chrt --fifo 80 /home/test001/sleep_on_nic_clock1

## test run using nic clock
# start time = 1635853936378080682, end_time=1635853937378080682, curr_ns=1635853937378081818, cycles=140719,   diff(curr-end)=1136
# start time = 1635853937378127226, end_time=1635853938378127226, curr_ns=1635853938378129274, cycles=133578,   diff(curr-end)=2048
# start time = 1635853938378158554, end_time=1635853939378158554, curr_ns=1635853939378158938, cycles=133578,   diff(curr-end)=384
# start time = 1635853939378187354, end_time=1635853940378187354, curr_ns=1635853940378192298, cycles=133026,   diff(curr-end)=4944
# start time = 1635853940378221738, end_time=1635853941378221738, curr_ns=1635853941378228090, cycles=133649,   diff(curr-end)=6352
# start time = 1635853941378255994, end_time=1635853942378255994, curr_ns=1635853942378259562, cycles=133100,   diff(curr-end)=3568
# start time = 1635853942378288378, end_time=1635853943378288378, curr_ns=1635853943378292810, cycles=133638,   diff(curr-end)=4432
# start time = 1635853943378322826, end_time=1635853944378322826, curr_ns=1635853944378325562, cycles=133073,   diff(curr-end)=2736
# start time = 1635853944378354330, end_time=1635853945378354330, curr_ns=1635853945378355882, cycles=133634,   diff(curr-end)=1552
# start time = 1635853945378384490, end_time=1635853946378384490, curr_ns=1635853946378387034, cycles=133037,   diff(curr-end)=2544

## test run using CLOCK_MONOTONIC
# start time = 2761980619832150, end_time=2761981619832150, curr_ns=2761981619832180, cycles=11911788,  diff(curr-end)=30
# start time = 2761981619853612, end_time=2761982619853612, curr_ns=2761982619853682, cycles=11904294,  diff(curr-end)=70
# start time = 2761982619876436, end_time=2761983619876436, curr_ns=2761983619876438, cycles=11856345,  diff(curr-end)=2
# start time = 2761983619898473, end_time=2761984619898473, curr_ns=2761984619898521, cycles=11905893,  diff(curr-end)=48
# start time = 2761984619921518, end_time=2761985619921518, curr_ns=2761985619921576, cycles=11847840,  diff(curr-end)=58
# start time = 2761985619943039, end_time=2761986619943039, curr_ns=2761986619943109, cycles=11905781,  diff(curr-end)=70
# start time = 2761986619964716, end_time=2761987619964716, curr_ns=2761987619964732, cycles=11853388,  diff(curr-end)=16
# start time = 2761987619990173, end_time=2761988619990173, curr_ns=2761988619990239, cycles=11906530,  diff(curr-end)=66
# start time = 2761988620012393, end_time=2761989620012393, curr_ns=2761989620012399, cycles=11857035,  diff(curr-end)=6
# start time = 2761989620035020, end_time=2761990620035020, curr_ns=2761990620035080, cycles=11896733,  diff(curr-end)=60

## test run using CLOCK_REALTIME
# start time = 1635853977432626806, end_time=1635853978432626806, curr_ns=1635853978432626835, cycles=11909804, diff(curr-end)=29
# start time = 1635853978432648669, end_time=1635853979432648669, curr_ns=1635853979432648722, cycles=11856100, diff(curr-end)=53
# start time = 1635853979432672061, end_time=1635853980432672061, curr_ns=1635853980432672122, cycles=11899583, diff(curr-end)=61
# start time = 1635853980432699242, end_time=1635853981432699242, curr_ns=1635853981432699306, cycles=11845573, diff(curr-end)=64
# start time = 1635853981432724632, end_time=1635853982432724632, curr_ns=1635853982432724705, cycles=11910562, diff(curr-end)=73
# start time = 1635853982432746795, end_time=1635853983432746795, curr_ns=1635853983432746813, cycles=11857330, diff(curr-end)=18
# start time = 1635853983432768427, end_time=1635853984432768427, curr_ns=1635853984432768450, cycles=11905325, diff(curr-end)=23
# start time = 1635853984432790964, end_time=1635853985432790964, curr_ns=1635853985432791036, cycles=11854323, diff(curr-end)=72
# start time = 1635853985432816708, end_time=1635853986432816708, curr_ns=1635853986432816741, cycles=11897911, diff(curr-end)=33
# start time = 1635853986432841581, end_time=1635853987432841581, curr_ns=1635853987432841585, cycles=11899427, diff(curr-end)=4
*/


/*
 * sleep_on_nic_clock1 - sleep on network card clock
 *
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <sched.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>


#ifndef CLOCK_INVALID
#define CLOCK_INVALID -1
#endif

#define NSEC_PER_SEC (1000000000LL)


static
clockid_t get_clockid(int fd)
{
        const int CLOCKFD = 3;

        return (((unsigned int) ~fd) << 3) | CLOCKFD;
}

signed long long timespec2ns(struct timespec *ts)
{
        signed long long ns;

        ns = ts->tv_nsec + (ts->tv_sec * NSEC_PER_SEC);

        return(ns);
}

void ns2timespec(signed long long ns, struct timespec *ts)
{
        lldiv_t lld;

        lld = lldiv(ns, NSEC_PER_SEC);
        ts->tv_sec  = lld.quot;
        ts->tv_nsec = lld.rem;
}

int clock_gettime_ns(clockid_t clockid, signed long long *ns)
{
        int res;
        struct timespec ts;

        res = clock_gettime(clockid, &ts);
        if (res == 0)
                *ns = timespec2ns(&ts);

        return(res);
}


void test_busysleep_on_clock(clockid_t clkid, double delay)
{
        signed long long ns, start_ns, end_ns;
        long cycles;

        /* cycle scheduler so it generates less interference */
        (void)sched_yield();

        (void)clock_gettime_ns(clkid, &start_ns);

        end_ns = start_ns + NSEC_PER_SEC * delay;
        ns = start_ns;

        for(cycles = 0 ; ns < end_ns ; cycles++)
        {
                (void)clock_gettime_ns(clkid, &ns);
        }

        (void)printf("# start time = %lld, end_time=%lld, curr_ns=%lld, cycles=%ld,\tdiff(curr-end)=%lld\n",
                start_ns, end_ns, ns, cycles, (ns-end_ns));
}


int main(int ac, char *av[])
{
        int fd;
        clockid_t clkid;
        const char *devicename = "/dev/ptp0";

        /*
         * todo: socket fd to /dev/ptpX filename should be implemented here
         */

        fd = open(devicename, O_RDWR);
        if (fd < 0) {
                (void)fprintf(stderr, "opening %s: %s\n", devicename,
                        strerror(errno));
                return(EXIT_FAILURE);
        }

        clkid = get_clockid(fd);
        if (CLOCK_INVALID == clkid) {
                (void)fprintf(stderr, "failed to read clock id\n");
                return(EXIT_FAILURE);
        }

        (void)puts("/*");

#if 1/* TEST_CLOCK_NANOSLEEP_ON_NIC */
        int i;

        (void)printf("\n## test run using nic clock\n");
        for(i=0 ; i < 10 ; i++)
                test_busysleep_on_clock(clkid, 1.0);

        (void)printf("\n## test run using CLOCK_MONOTONIC\n");
        for(i=0 ; i < 10 ; i++)
                test_busysleep_on_clock(CLOCK_MONOTONIC, 1.0);

        (void)printf("\n## test run using CLOCK_REALTIME\n");
        for(i=0 ; i < 10 ; i++)
                test_busysleep_on_clock(CLOCK_REALTIME, 1.0);

#endif /* TEST_CLOCK_NANOSLEEP_ON_NIC */

        (void)close(fd);
        (void)puts("*/");

        return(EXIT_SUCCESS);
}