netdev - Re: [PATCH bpf-next v2 2/6] xdp: introduce xdp

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Message-ID: <CAJ+HfNhFERV+xE7EUup-tu_nBTTqG=7L8bWm+W8h_Lzth4zuKQ@mail.gmail.com>
Date:   Mon, 25 Nov 2019 16:21:46 +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>,
        Björn Töpel <bjorn.topel@...el.com>,
        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>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: Re: [PATCH bpf-next v2 2/6] xdp: introduce xdp_call

On Mon, 25 Nov 2019 at 12:18, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Björn Töpel <bjorn.topel@...il.com> writes:
>
> > From: Björn Töpel <bjorn.topel@...el.com>
> >
> > The xdp_call.h header wraps a more user-friendly API around the BPF
> > dispatcher. A user adds a trampoline/XDP caller using the
> > DEFINE_XDP_CALL macro, and updates the BPF dispatcher via
> > xdp_call_update(). The actual dispatch is done via xdp_call().
> >
> > Note that xdp_call() is only supported for builtin drivers. Module
> > builds will fallback to bpf_prog_run_xdp().
>
> I don't like this restriction. Distro kernels are not likely to start
> shipping all the network drivers builtin, so they won't benefit from the
> performance benefits from this dispatcher.
>
> What is the reason these dispatcher blocks have to reside in the driver?
> Couldn't we just allocate one system-wide, and then simply change
> bpf_prog_run_xdp() to make use of it transparently (from the driver
> PoV)? That would also remove the need to modify every driver...
>

Good idea! I'll try that out. Thanks for the suggestion!

Björn


> -Toke
>