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Date:   Wed, 11 Dec 2019 13:38:01 +0100
From:   Björn Töpel <>
To:     Toke Høiland-Jørgensen <>
Cc:     Netdev <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        bpf <>,
        Magnus Karlsson <>,
        "Karlsson, Magnus" <>,
        Jonathan Lemon <>,
        Edward Cree <>,
        Toke Høiland-Jørgensen <>,
        Andrii Nakryiko <>
Subject: Re: [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher

On Mon, 9 Dec 2019 at 18:42, Björn Töpel <> 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

> Björn
> > -Toke
> >

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