[ntp:questions] A proposal to use NIC launch time support to improve NTP

Brian Utterback brian.utterback at oracle.com
Thu Dec 13 13:23:47 UTC 2012


On 12/13/2012 5:00 AM, Jonatan Walck wrote:
>> This is going to be very hard to get it to be useful. Looking at
>> >the specs for the card, the timestamp you give is relative to a
>> >clock that is internal to the controller, and is only accurate to
>> >the nearest second. That is, it is like the PPS in that it is
>> >assumed that the clock is in sync to within .5 seconds to avoid
>> >aliasing the timestamp.
>> >
>> >Brian.
> The internal clock of the network controller is the PHC for IEEE1588,
> it has a 1 ns resolution, and can be steered with a 32 bit fractional
> of 1 ns. see SYSTIML and TIMINCA in the I210 datasheet.
>
> // jwalck

I know that. The problem is that there is going to be jitter introduced 
when you set the clock from the kernel. That is generally the problem 
with IEEE 1588, getting the time from the controller to the kernel and 
vice versa. If you have to go across a PCI bus for instance that will 
introduce jitter.

Brian


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