Re: network misbehaviour with gplpv and 2.6.30

[Paul Durrant <paul.durrant@citrix.com>]

James Harper wrote:
> 
>> 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
> Andrew?).
> 

It's not unusual for h/w drivers to support 'LRO', i.e. they re-assemble 
consecutive in-order TCP segments into a large packet before passing up 
the stack. I believe that these would manifest themselves as TSOs coming 
into the transmit side of netback, just as locally originated large 
packets would.

> 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.
> 

Yes, a tcpdump of what's being passed into netback in dom0 should tell 
us what's happening.

   Paul

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