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

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Date:   Fri, 18 Nov 2022 01:29:15 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.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

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> 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.

I'm ~90% sure we'll need that optimisation, but OK, we can start from a
baseline of having them be function calls...

-Toke