netdev - Re: [xdp-hints] Re: [PATCH bpf-next 05/11] veth: Support rx timestamp metadata for xdp

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Date:   Thu, 17 Nov 2022 16:02:54 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [xdp-hints] Re: [PATCH bpf-next 05/11] veth: Support rx timestamp
 metadata for xdp

On Thu, Nov 17, 2022 at 3:46 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> >
> > Ack. I can replace the unrolling with something that just resolves
> > "generic" kfuncs to the per-driver implementation maybe? That would at
> > least avoid netdev->ndo_kfunc_xxx indirect calls at runtime..
>
> As stated above, I think we should keep the unrolling. If we end up with
> an actual CALL instruction for every piece of metadata that's going to
> suck performance-wise; unrolling is how we keep this fast enough! :)

Let's start with pure kfuncs without requiring drivers
to provide corresponding bpf asm.
If pure kfuncs will indeed turn out to be perf limiting
then we'll decide on how to optimize them.