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

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Date:   Wed, 11 Dec 2019 13:38:01 +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 18:42, Björn Töpel <bjorn.topel@...il.com> wrote:
>
[...]
> > 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.
>

Toke, I tried to measure the impact, but didn't really get anything
useful out. :-(

My concern was mainly that text-poking is a point of contention, and
it messes with the icache. As for contention, we're already
synchronized around the rtnl-lock. As for the icache-flush effects...
well... I'm open to suggestions how to measure the impact in a useful
way.

>
> Björn
>
> > -Toke
> >