Re: [PATCH v4 2/2] gro: optimise redundant parsing of packets

Eric Dumazet
2023-03-22T10:11:34Z

On Wed, Mar 22, 2023 at 2:59 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Mon, 2023-03-20 at 18:00 +0100, Richard Gobert wrote:
> > Currently the IPv6 extension headers are parsed twice: first in
> > ipv6_gro_receive, and then again in ipv6_gro_complete.
> >
> > By using the new ->transport_proto field, and also storing the size of the
> > network header, we can avoid parsing extension headers a second time in
> > ipv6_gro_complete (which saves multiple memory dereferences and conditional
> > checks inside ipv6_exthdrs_len for a varying amount of extension headers in
> > IPv6 packets).
> >
> > The implementation had to handle both inner and outer layers in case of
> > encapsulation (as they can't use the same field). I've applied a similar
> > optimisation to Ethernet.
> >
> > Performance tests for TCP stream over IPv6 with a varying amount of
> > extension headers demonstrate throughput improvement of ~0.7%.
>
> I'm surprised that the improvement is measurable: for large aggregate
> packets a single ipv6_exthdrs_len() call is avoided out of tens calls
> for the individual pkts. Additionally such figure is comparable to
> noise level in my tests.
>
> This adds a couple of additional branches for the common (no extensions
> header) case.
>
> while patch 1/2 could be useful, patch 2/2 overall looks not worthy to
> me.
>
> I suggest to re-post for inclusion only patch 1, unless others have
> strong different opinions.
>

+2

I have the same feeling/opinion.

> Cheers,
>
> Paolo
>