| Re: [chrony-dev] SW/HW timestamping on Linux |
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On Fri, Nov 18, 2016 at 03:37:07PM +0100, Miroslav Lichvar wrote:
> On Thu, Nov 17, 2016 at 05:44:23PM -0800, Denny Page wrote:
> > Although reduced, I’m still seeing spikes with the patch below.
>
> I'm not sure what could be wrong at this point. Maybe it really is a
> kernel or HW issue. I'm wondering what would be the best way to
> confirm or reject that idea.
I think I finally found what was causing the spikes for you. There was
a typo in the code that was processing raw PHC readings, which
effectively disabled filtering of delayed readings and added a
significant error to the PHC sample time. It explains why the results
I was seeing were not quite as good as I expected. Maybe because I'm
testing on a machine with a faster CPU, it looked more like noise than
spikes.
It should be now fixed in git. Please test. If you were doing any
experiments comparing offsets between SW and HW timestamping, you will
probably need to start again as this bug effectively added an offset
of maybe 1-3 microseconds. I'm sorry it took so long to figure it out.
--
Miroslav Lichvar
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