So first of all PTP doesn't compensate for anything at all is that right? (Is there a way todo this automatically?) Found out that the delay i210 with another i210 is pretty consistent (very few nanoseconds). It cancels only out if i have two completly identical card's?
That the intel driver speaks not a hundred percent proof is definitfly a thing. Now i would need to proof which of them produces more in/egress latency. Von: Miroslav Lichvar <mlich...@redhat.com> An: Richard Cochran <richardcoch...@gmail.com> Kopie: Armin HAMAR <armin.ha...@sprecher-automation.com>, Linuxptp-users@lists.sourceforge.net Datum: 03.07.2019 08:06 Betreff: Re: [Linuxptp-users] PPS to Linux PTP offset/delay? On Tue, Jul 02, 2019 at 09:31:44AM -0700, Richard Cochran wrote: > On Tue, Jul 02, 2019 at 09:36:50AM +0200, Miroslav Lichvar wrote: > > So, with two > > directly connected I210s (short cable) the measured delay should be > > close to zero. > > That is true of any two devices, since the tx/rx asymmetry cancels out > (even without any corrections applied). The error in the measured offset cancels out between any two identical NICs, but the measured PTP delay is a sum of the TX and RX timestamping errors (and the delay in the cable). For example between two I350s on 1Gb I see a delay of 507 ns. An offset I measured between an I210 (using the igb compensation) and I350 in the same computer over PCIe is about 240 ns, so the TX/RX error of the I350 seems to be very asymmetric too. -- Miroslav Lichvar
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