On Wed, Dec 07, 2016 at 06:20:48PM +0100, Miroslav Lichvar wrote:
> Yes, I think that might be helpful. I spent some time today comparing
> your method with the current code and at least on my system with i210
> I see a shift in the distribution of the offset to one side when the
> network is (heavily) loaded. Compare these two histograms
> 
> http://i.imgur.com/GsRwhyX.png (min delay * 1.1)
> http://i.imgur.com/MHYRCCx.png (min delay + sys_prec)
> 
> Here is a scattergram of the offset vs delay, ignoring the first
> reading. It shows there is a strong asymmetry.
> 
> http://i.imgur.com/EgPL9mH.png

Denny,

there is apparently a new ioctl for measuring the offset between the
NIC clock and system clock, which is supported on some onboard NICs
(that share clock with the CPU?). It's called PTP_SYS_OFFSET_PRECISE
and if I understand how it works correctly, it should solve all these
problems with delay and asymmetry. Is it supported on the i211 or
i350?

-- 
Miroslav Lichvar

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