[ntp:questions] 1Gb/s network issues - was: Re: OT: GPS18x LVC failure

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Tue Oct 13 07:25:33 UTC 2009


"Kasper Pedersen" <> wrote in message 
news:4ad360ef$0$36567$edfadb0f at dtext01.news.tele.dk...
[]
> I built a device that spits out priority tagged ethernet frames with 
> <200ns error to UTC, and did a number of tests with different networks 
> and nics, the result of which is in a table here:
>
>   http://n1.taur.dk/etherpps/
>
> On switches that understand priority tagging it makes a world of 
> difference. On the corporate network where I had 14us unaccounted 
> latency and 18us jitter with the packet prioritized above all other 
> traffic, when the prioritization was disabled I got another 200us jitter 
> at peak load time (users and iscsi traffic sharing the same path).
>
> I suppose there's a way to make the kernel priority tag outbound ntp 
> packets, but I did not find it.
>
> /Kasper Pedersen

Many thanks for posting that, Kasper, most interesting!

David 




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