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xen-devel
Re: [Xen-devel] [PATCH] Network Checksum Removal
On Wednesday 25 May 2005 04:14 pm, Keir Fraser wrote:
> On 25 May 2005, at 21:06, Ian Pratt wrote:
> >> There is a patch on netdev which can decrease the CPU load of
> >> bridging.
> >> specifically, it allows the bridge device to take advantage
> >> of the network device features (like hardware checksum
> >> offload). Stephen Hemminger says it should go in the 2.6.13 kernel.
> >
> > Please can you post it as a patch so that we can include it in our
> > 2.6.11 patches directory.
> >
> > With the patch, csum offload will be much more interesting in the rx
> > case
>
> The code we already have offloads rx csums both for dom0 and domU's
> (the dom0 traffic has to be received through veth0 though, not the
> bridge device itself).
The problem with the bridge device is that all traffic generated in dom0 will
be software checksummed, regardless of whether it needs to be or not. In
Xen's case, it will software checksum all traffic to domU, even though the
vif device is advertising NETIF_F_NO_CSUM.
This is because the stack doesn't see the features of the children devices of
the bridge, only the features of the bridge device itself. I created a quick
hack to work around this, and started the discussion on the Linux netdev
mailing list about how to fix the problem. From this discussion, a patch was
created which does most of what we want, but needs to be slightly modified to
be optimal for Xen. I will post the Xen optimized patch as soon as I have it
done.
Thanks,
Jon
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