netdev - Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher

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Date:   Fri, 13 Dec 2019 09:23:06 +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>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher

On Wed, 11 Dec 2019 at 14:26, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> [...]
> > +/* The BPF dispatcher is a multiway branch code generator. The
> > + * dispatcher is a mechanism to avoid the performance penalty of an
> > + * indirect call, which is expensive when retpolines are enabled. A
> > + * dispatch client registers a BPF program into the dispatcher, and if
> > + * there is available room in the dispatcher a direct call to the BPF
> > + * program will be generated. All calls to the BPF programs called via
> > + * the dispatcher will then be a direct call, instead of an
> > + * indirect. The dispatcher hijacks a trampoline function it via the
> > + * __fentry__ of the trampoline. The trampoline function has the
> > + * following signature:
> > + *
> > + * unsigned int trampoline(const void *xdp_ctx,
> > + *                         const struct bpf_insn *insnsi,
> > + *                         unsigned int (*bpf_func)(const void *,
> > + *                                                  const struct bpf_insn *));
> > + */
>
> Nit: s/xdp_ctx/ctx/
>

Thanks! Same type-o in the DEFINE/DECLARE macros. Will fix in v5.


Björn


> -Toke
>