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

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> >
> > 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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