RE: [Xen-devel] Network drop on domU (netfront: rx->offset: 0, size: 4294967295)

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

> 
> Not sure, it will help :-
> 
> http://hightechsorcery.com/2008/03/virtualization-tip-always-disable-
> checksumming-virtual-ethernet-devices
> 
> Personally , i used to manage this way.
> 

When it works, checksum offload and [GTL]SO can make a big difference in
performance when the packets are staying inside the same physical
machine, and can still make a big difference even when they are leaving
via a physical adapter.

Two servers I look after have no problems at all with checksum or large
send offloads.

One server gets upset though and forgets to make the checksums correct
when it routes the packets over a GRE tunnel. It's strange though - it
will be fine for weeks and then suddenly starts forgetting to fix up the
checksums for 30 minutes or so, then comes good again.

If network performance isn't a big part of what you are doing (eg your
VM is serving web pages at mbit rather than gbit speeds), then turning
off the offloads is probably reasonable. If you are doing file serving
or something then it's probably worth finding a configuration that
works.

It can be horribly frustrating though - I recently spent hours on a
non-virtualised windows server that was hanging connections all over the
place. It turned out to be a checksum offload problem and turning off
the feature on the card fixed it. I think it was an interaction with the
firewall or something.

James

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel