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

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Tue, Nov 15, 2016 at 08:24:37PM -0800, Denny Page wrote:
> With the latest drop in the repo, I’m still seeing the wild spikes in the standard deviation with hardware time stamping against the fast responding hardare units. I'm also still seeing a better base deviation using software timestamps against them as well.
> 
> I do see better results with hardware time stamping when doing chrony to chrony, but I believe that this is a result of the general purpose computers being a bit slower to respond than the dedicated hardware units.

Hm, the fix helped with the spikes I was seeking. Did we rule out the
possibility that in your case the spikes are due to the other issue with
out-of-order HW timestamps? Could you try it with this patch to make
sure only measurements with HW timestamps are used?

--- a/ntp_core.c
+++ b/ntp_core.c
@@ -1434,6 +1434,9 @@ receive_packet(NCR_Instance inst, NTP_Local_Address *local_addr,
        prevent a synchronisation loop */
     testD = message->stratum <= 1 || REF_GetMode() != REF_ModeNormal ||
             pkt_refid != UTI_IPToRefid(&local_addr->ip_addr);
+
+    if (inst->local_tx.source != NTP_TS_HARDWARE || rx_ts->source != NTP_TS_HARDWARE)
+      testB = 0;
   } else {
     offset = delay = dispersion = 0.0;
     sample_time = rx_ts->ts;

-- 
Miroslav Lichvar

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