RE: [Xen-devel] ip/udp checksum offload from minios guest

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Wed, 2011-03-30 at 11:37 +0100, James Harper wrote:
> > > Is IPv6 offload (gso and/or checksum) supported at this time?
> > 
> > For GSO only TCPv4 is supported.
> > 
> > For checksum only TCPv4 and UDPv4 are supported.
> > 
> > Extending netback to cover more cases would be relatively trivial, I
> > think. e.g. extending checksum_setup and/or netbk_set_skb_gso in
> > netback.c, plus doing the opposite same on the guest RX paths.
> > 
> > I suspect most of the complexity will probably come from the correct
> > negotiation of the featureset via xenstore ;-)
> > 
> 
> Yes. Given the problems I've seen under linux with offload it would be
> nice to have even more granularity than we do now. We'd definitely
> want to be able to turn offload on and off for all combinations of
> tcp/udp/csum/gso individually in case there is a problem somewhere.

Absolutely. Paul Durrant made some improvements in this area not so long
ago. Also from the looks of things upstream have recently separated out
the concept of what the h/w supports from what is actually currently
configured to be enabled which should be useful going forward.

> The main problem I've seen is that Linux doesn't seem to understand
> that my network card supports offload functions but not in combination
> with VLAN, so only the untagged packets (eg vlan1) can be offloaded.
> That was back at 2.6.18 so hopefully the support is better now.

I should hope so ;-)

In Linux a VLAN device is a new net device which sits on top of the
physical device and has it's own offload settings etc so at least there
is a route to fixing it there...

Ian



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