netdev - Re: [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher

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Message-ID: <CAJ+HfNjZnxrgYtTzbqj2VOP+5A81UW-7OKoReT0dMVBT0fQ1pg@mail.gmail.com>
Date:   Mon, 9 Dec 2019 18:42:22 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher

On Mon, 9 Dec 2019 at 16:00, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Björn Töpel <bjorn.topel@...il.com> writes:
>
[...]
>
> I like the new version where it's integrated into bpf_prog_run_xdp();
> nice! :)
>

Yes, me too! Nice suggestion!

> > The XDP dispatcher is always enabled, if available, because it helps
> > even when retpolines are disabled. Please refer to the "Performance"
> > section below.
>
> Looking at those numbers, I think I would moderate "helps" to "doesn't
> hurt" - a difference of less than 1ns is basically in the noise.
>
> You mentioned in the earlier version that this would impact the time it
> takes to attach an XDP program. Got any numbers for this?
>

Ah, no, I forgot to measure that. I'll get back with that. So, when a
new program is entered or removed from dispatcher, it needs to be
re-jited, but more importantly -- a text poke is needed. I don't know
if this is a concern or not, but let's measure it.


Björn

> -Toke
>