Re: [Ptpd-announce] [Ptpd-devel] 802.3 (Ethernet) mode for clients and PCAP support added to the trunk...

[Wojciech O. <woj...@ow...>]

George,

It's similar on Linux - PCAP gets the data even before they hit IPFilter /
IPTables - straight off the driver. The latest pcap versions allow you to
set the timestamp resolution (using arbitrary keywords like HIGH/LOW) but I
still need to establish if you can get ns resolution in the newer kernels.

So basically very similar to FreeBSD, however I'm not sure how the
performance actually compares. The SyncLab / RADClock guys did some
benchmarks with BPF included, but Linux unfortunately was not tested.

Regards
Wojciech


On 27 May 2013 02:36, George Neville-Neil <gn...@ne...> wrote:

>
> On May 26, 2013, at 18:33 , Wojciech Owczarek <woj...@ow...>
> wrote:
>
> > George, All,
> >
> > I just submitted some minor fixes to the PCAP code - tested on Linux:
> RHEL6 and Ubuntu. Hybrid and unicast modes should be working OK with PCAP
> now [ only slave mode tested! ]
> >
>
> Great, I'll check them on FreeBSD in the next day or so.
>
> > Naturally PCAP works fine on Linux. I don't think there is a more
> portable solution in userspace.
> >
> > Observations so far:
> >
> > - accuracy improved by approx 5us straight away, precision improved as
> well due to lower jitter
> > - unfortunately servo output will be a little jittery (short-term jitter
> in smaller scale - "thicker" plots basically), reason being that pcap we're
> back to microsecond timestamp resolution - not much can be done about it it
> seems, even with the latest libpcap
> > - need to double check socket initialisation and handling when using
> pcap: ptpd is currently bounding back ICMP unreachables in reaction to
> unicast delay responses. Doesn't break anything on the slave side but
> shouldn't be happening.
>
> So one thing that will happen on FreeBSD, but I"m not sure on Linux is
> that with BPF
> we take the timestamp right above the network driver, before any other
> part of the system
> sees the packet.  That was one of my main motivations for doing that.  The
> other thing
> that will eventually go into the code is that BPF/PCAP on FreeBSD can now
> have
> nanosecond timestamps, as of FreeBSD 10 (CURRENT).  Once I test that I'll
> add those
> switches to the code.
>
> Best,
> George
>
>


-- 
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Wojciech Owczarek