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From:   Eric Dumazet <edumazet@google.com>
Date:   Wed, 22 Mar 2023 03:11:18 -0700
Message-ID: <CANn89iK_bsPoaRVe+FNZ7LF_eLbz2Af6kju4j9TVHtbgkpcn5g@mail.gmail.com>
Subject: Re: [PATCH v4 2/2] gro: optimise redundant parsing of packets
To:     Paolo Abeni <pabeni@redhat.com>
Cc:     Richard Gobert <richardbgobert@gmail.com>, davem@davemloft.net,
        kuba@kernel.org, dsahern@kernel.org, alexanderduyck@fb.com,
        lucien.xin@gmail.com, lixiaoyan@google.com, iwienand@redhat.com,
        leon@kernel.org, ye.xingchen@zte.com.cn, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Wed, Mar 22, 2023 at 2:59=E2=80=AFAM Paolo Abeni <pabeni@redhat.com> wro=
te:
>
> 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 conditi=
onal
> > checks inside ipv6_exthdrs_len for a varying amount of extension header=
s 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 simila=
r
> > 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
>