> On Jan 18, 2017, at 09:11, Denny Page <dennyp...@me.com> wrote:
>> On Jan 18, 2017, at 05:43, Miroslav Lichvar <mlich...@redhat.com 
>> <mailto:mlich...@redhat.com>> wrote:
>> 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,
> Unfortunately, no. PTP_SYS_OFFSET_PRECISE uses PCIE_PTM (Precise Time 
> Measurement) which requires newer PCIe chipsets. I don’t have a system that 
> supports PTM. Best that I can tell, the only Ethernet driver in the kernel 
> that currently offers PTM support is the Intel PCI-Express pro/1000 (E1000E), 
> and I don’t have one of those either. Otherwise I would have added support 
> for it in ethtscal. :)
> https://pcisig.com/sites/default/files/specification_documents/ECN_PTM_Revision1a_31_Mar_2013.pdf
> <https://pcisig.com/sites/default/files/specification_documents/ECN_PTM_Revision1a_31_Mar_2013.pdf>
> Denny

And To be clear, this would not address phy/mac delay/asymmetry issues. It 
would just replace the call to PTP_SYS_OFFSET. Instead of an array that you 
have to interpolate, you just get a single (accurate) value. This would be very 
helpful however, because PTP_SYS_OFFSET is the source of most of the variance 
in ethtscal.


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