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RE: [Xen-devel] network misbehaviour with gplpv and 2.6.30

To: "Paul Durrant" <paul.durrant@xxxxxxxxxx>
Subject: RE: [Xen-devel] network misbehaviour with gplpv and 2.6.30
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Tue, 21 Jul 2009 20:05:41 +1000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Andrew Lyon <andrew.lyon@xxxxxxxxx>
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Thread-index: AcoJ5qngkzzofF+IR3a70YHDOQvBLgAA2IVg
Thread-topic: [Xen-devel] network misbehaviour with gplpv and 2.6.30
> James Harper wrote:
> > With GPLPV under 2.6.30, GPLPV gets the following from the ring:
> >
> > ring slot n (first buffer):
> >  status (length) = 54 bytes
> >  offset = 0
> >  flags = NETRXF_extra_info (possibly csum too but not relevant)
> > ring slot n + 1 (extra info)
> >  gso.size (mss) = 1460
> >
> > Because NETRXF_extra_info is not set, that's all I get for that
> I assume you mean NETRXF_more_data here?

Oops. Yes, that's exactly what I mean.

> Are you saying that ring slot n
> has only NETRXF_extra_info and *not* NETRXF_more_data?

Yes. From the debug I have received from Andrew Lyon, NETRXF_more_data
is _never_ set.

>From what Andrew tells me (and it's not unlikely that I misunderstood),
the packets in question come from a physical machine external to the
machine running xen. I can't quite understand how that could be as they
are 'large' packets (>1514 byte total packet length) which should only
be locally originated. Unless he's running with jumbo frames (are you

I've asked for some more debug info but he's in a different timezone to
me and probably isn't awake yet. I'm less and less inclined to think
that this is actually a problem with GPLPV and more a problem with
netback (or a physical network driver) in 2.6.30, but a tcpdump in Dom0,
HVM without GPLPV and maybe in a Linux DomU should tell us more.



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