RE: [Xen-users] Slow TCP performance between Windows VistaandXenPV-on-HVM guest

["Fischer, Anna" <anna.fischer@xxxxxx>]

I haven't followed your email thread, but the bug I am talking about is purely 
related to the TCP connection tracking module in the Dom0 kernel. If you are 
not using NAT at all then you will probably have a different issue. The problem 
is potentially also very specific to the Dom0 kernel you/I run, I run Novel 
SLES 10 Xen which is some modified 2.6.16 kernel. I have not yet tracked down 
the exact kernel code lines that are causing this bug.

Anna

> -----Original Message-----
> From: Ian Tobin [mailto:itobin@xxxxxxxxxxxxx]
> Sent: 15 June 2010 09:53
> To: James Harper; Fischer, Anna; Robert Dunkley; xen-
> users@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-users] Slow TCP performance between Windows
> VistaandXenPV-on-HVM guest
> 
> Hi,
> 
> Does this have any relevance to my issue?
> 
> Ian
> 
> 
> 
> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of James Harper
> Sent: 15 June 2010 05:54
> To: Fischer, Anna; Robert Dunkley; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-users] Slow TCP performance between Windows
> VistaandXenPV-on-HVM guest
> 
> > >
> > > Hardware offload is disabled on the NIC inside the Linux guest, on
> the
> > > VIF in Dom0 and also on the NIC in Dom0. All offload features,
> including
> > > checksum offload. My guess was also that this must be the problem,
> as I
> > > said before it actually works with exactly the same guest running on
> > > VMWare. But obviously on VMWare it doesn't run the Xen
> netfront/netback
> > > drivers, so my guess was that some configuration on there might be
> the
> > > issue. But as I said, switching off hardware offload does not make
> any
> > > difference at all. At the moment it does not run any HW offloading.
> > >
> >
> > I have found out by now that the problem is a bug in the NAT function
> in Dom0,
> > e.g. in the TCP connection tracking module. It fails to rewrite
> Delayed ACK
> > packets from newer Windows (Vista / 7) machines. When I configure the
> Windows
> > TCP stack with TCP_NODELAY then it all works.
> >
> 
> Thanks for posting that! Do you know if the problem is resolved in newer
> kernels?
> 
> James
> 
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> 


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