Re: [chrony-dev] SW/HW timestamping on Linux

[Denny Page <dennypage@xxxxxx>]

I’m still chasing the offset issue. However on the spikes/noise issue, the patch below addresses the noise and low level spikes that I was seeing. I was seeing errors of 2-60ns off in the average offset for the nic clock, which this corrects. I’m still seeing the occasional larger spike, but this does not appear to be related to issues with PTP_SYS_OFFSET. I’m speculating that the large spikes are associated with the kernel preemption, but haven’t had time to test this theory.

Denny


*** ntp_io_linux.c.org  Wed Nov 23 08:41:54 2016
--- ntp_io_linux.c      Sun Dec  4 22:32:45 2016
***************
*** 288,295 ****
  {
    struct ptp_sys_offset sys_off;
    struct timespec ts1, ts2, ts3, phc_tss[PHC_READINGS], sys_tss[PHC_READINGS];
!   double min_delay = 0.0, delays[PHC_READINGS], phc_sum, local_sum, local_prec;
!   int i, n;
  
    /* Silence valgrind */
    memset(&sys_off, 0, sizeof (sys_off));
--- 288,295 ----
  {
    struct ptp_sys_offset sys_off;
    struct timespec ts1, ts2, ts3, phc_tss[PHC_READINGS], sys_tss[PHC_READINGS];
!   double delays[PHC_READINGS], delay_limit, delay_sum, offset_sum;
!   int min_delay = 0, i, n;
  
    /* Silence valgrind */
    memset(&sys_off, 0, sizeof (sys_off));
***************
*** 317,344 ****
        /* Step in the middle of a PHC reading? */
        return 0;
  
!     if (!i || delays[i] < min_delay)
!       min_delay = delays[i];
    }
  
-   local_prec = LCL_GetSysPrecisionAsQuantum();
- 
    /* Combine best readings */
!   for (i = n = 0, phc_sum = local_sum = 0.0; i < PHC_READINGS; i++) {
!     if (delays[i] > min_delay + local_prec)
        continue;
  
!     phc_sum += UTI_DiffTimespecsToDouble(&phc_tss[i], &phc_tss[0]);
!     local_sum += UTI_DiffTimespecsToDouble(&sys_tss[i], &sys_tss[0]) + delays[i] / 2.0;
      n++;
    }
  
    assert(n);
  
!   UTI_AddDoubleToTimespec(&phc_tss[0], phc_sum / n, phc_ts);
!   UTI_AddDoubleToTimespec(&sys_tss[0], local_sum / n, &ts1);
    LCL_CookTime(&ts1, local_ts, NULL);
!   *p_delay = min_delay;
  
    return 1;
  }
--- 317,345 ----
        /* Step in the middle of a PHC reading? */
        return 0;
  
!     if (delays[i] < delays[min_delay])
!       min_delay = i;
    }
  
    /* Combine best readings */
!   delay_limit = delays[min_delay] * 1.1;
!   for (i = n = 0, delay_sum = offset_sum = 0.0; i < PHC_READINGS; i++) {
!     if (delays[i] > delay_limit)
        continue;
  
!     delay_sum += delays[i];
!     UTI_AddDoubleToTimespec(&sys_tss[i], delays[i] / 2.0, &ts1);
!     offset_sum += UTI_DiffTimespecsToDouble(&phc_tss[i], &ts1);
      n++;
    }
  
    assert(n);
  
!   ts1 = sys_tss[min_delay];
!   UTI_AddDoubleToTimespec(&ts1, offset_sum / n, phc_ts);
! 
    LCL_CookTime(&ts1, local_ts, NULL);
!   *p_delay = delays[min_delay];
  
    return 1;
  }


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