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

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Message-ID: <CAJ+HfNhN+0n1XAZ8-fvH9EDL44aEAfuhWHKOPzqfoavM9h+-nQ@mail.gmail.com>
Date:   Tue, 10 Dec 2019 20:59:45 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     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>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher

On Mon, 9 Dec 2019 at 14:55, Björn Töpel <bjorn.topel@...il.com> wrote:
>
[...]
>
> Discussion/feedback
> ===================
>
> My measurements did not show any improvements for the jump target 16 B
> alignments. Maybe it would make sense to leave alignment out?
>

I did a micro benchmark with "test_progs -t xdp_prog" for all sizes
(max 48 aligned, max 64 non-aligned) of the dispatcher. I couldn't
measure any difference at all, so I will leave the last patch out
(aligning jump targets). If a workload appears where this is
measurable, it can be added at that point.

The micro benchmark also show that it makes little sense disabling the
dispatcher when "mitigations=off". The diff is within 1ns(!), when
mitigations are off. I'll post the data as a reply to the v4 cover
letter, so that the cover isn't clobbered with data. :-P

Björn