Re: [Xen-devel] [PATCH] Network Checksum Removal

[Jon Mason <jdmason@xxxxxxxxxx>]

On Thursday 26 May 2005 03:07 am, Keir Fraser wrote:
> On 26 May 2005, at 00:41, Jon Mason wrote:
> > The bridge device still is the device that the stack sees, and uses its
> > features to determine what to do during transmission.  If you monitor
> > the
> > skb->ip_summed flag going into netif_be_start_xmit(), you will see
> > that it is
> > 0 (meaning that the stack did the checksum in software).  Now if you
> > add the
> > following patch to the bridging device, you will notice that ip_summed
> > is now
> > being used.
>
> For local traffic transmitted via veth0, ip_summed is zero
> (CHECKSUM_NONE) at netif_be_start_xmit because the bridge forwarding
> code nobbles the ip_summed field. It does *not* checksum the packet:
> etherbridge never checksums packets it forwards because that is the
> destination's job (it's an end-to-end checksum at the protocol level).
>
> If you transmit local traffic directly on the bridge device then yes,
> you need a patch because it does not advertise NETIF_F_*_CSUM.

That is exactly the case I am refering to (sorry for the confusion).  The 
issue is not Xen sepcific (which is why I addressed the issue on the Linux 
networking mailing list), but Xen will see a boost when using the patch.

Thanks,
Jon


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