I read pcap packets in a loop and then try to timestamp those packets.

On a 2.6 kernel (e.g. centOs 6.8) it works correctly, but on 5.15 kernel (e.g. OEL 8) the time within 1 second hardly change 100µsec. Has this something to do with “NO_HZ: Reducing Scheduling-Clock Ticks” since there are more parameters in kernel 5.15 than in 2.6 the compiled program works correctly on my CentOs 6.8, but not on OEL 7 or 8.

Part of the code:

while((prec = pcap_next_ex(cap, &header, &pkt_data)) >= 0) {

    // more code

    // Time in msec
    struct timeval tv;
    time_t sec_midnight = time(NULL) % 86400;
    if(gettimeofday(&tv,NULL))
    {
        printf("ERRORn");
    }
    double usec = (double)tv.tv_usec;
    double frametime= (double)sec_midnight;
    frametime=frametime+usec/1000000.0;
    struct timespec ts;
    clock_gettime(CLOCK_REALTIME_COARSE, &ts);
    printf("Frametime = %f %f %in",frametime,usec,ts.tv_nsec);
}

Output of the program:

Frametime = 31139.900089 900089.000000 899621443
Frametime = 31139.900145 900145.000000 899621443
Frametime = 31139.900200 900200.000000 899621443
Frametime = 31139.900256 900256.000000 899621443
Frametime = 31139.900311 900311.000000 899621443
Frametime = 31139.900366 900366.000000 899621443
Frametime = 31139.900422 900422.000000 899621443
Frametime = 31139.900477 900477.000000 899621443
Frametime = 31139.900533 900533.000000 899621443
            ==> When the second changes, the usec changes with a big step.    
Frametime = 31140.543455 543455.000000 542621443
Frametime = 31140.543519 543519.000000 542621443
Frametime = 31140.543575 543575.000000 542621443
Frametime = 31140.543630 543630.000000 543621443
Frametime = 31140.543656 543656.000000 543621443
Frametime = 31140.543712 543712.000000 543621443
Frametime = 31140.543768 543768.000000 543621443
Frametime = 31140.543823 543823.000000 543621443
Frametime = 31140.543878 543878.000000 543621443