How precise is busy sleeping on nic clock ?
Posted by Anonymous on Tue 2nd Nov 2021 10:59
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view followups (newest first): How precise is busy sleeping on nic clock ? by Anonymous
modification of post by Anonymous (view diff)

        {
                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;
                ns = start_ns;

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

                printf("# start time = %lld\nend_time=%lld, curr_ns=%lld, diff(curr-end)=%lld\ncycles=%ld\n",
                        start_ns, end_ns, ns, (ns-end_ns), cycles);

        }

# chrt --fifo 80 ksh93 -c 'for((i=0 ; i < 10 ; i++)) ; do /home/test001/sleep_on_nic_clock1 | fgrep "diff(curr" ; done'
end_time=1635850618463770074, curr_ns=1635850618463776938, diff(curr-end)=6864
end_time=1635850619465874042, curr_ns=1635850619465879146, diff(curr-end)=5104
end_time=1635850620467940266, curr_ns=1635850620467946730, diff(curr-end)=6464
end_time=1635850621470062970, curr_ns=1635850621470063274, diff(curr-end)=304
end_time=1635850622472178202, curr_ns=1635850622472183802, diff(curr-end)=5600
end_time=1635850623474399306, curr_ns=1635850623474405114, diff(curr-end)=5808
end_time=1635850624476443562, curr_ns=1635850624476447770, diff(curr-end)=4208
end_time=1635850625478573274, curr_ns=1635850625478578474, diff(curr-end)=5200
end_time=1635850626480694570, curr_ns=1635850626480700730, diff(curr-end)=6160
end_time=1635850627482733914, curr_ns=1635850627482739002, diff(curr-end)=5088