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

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Date:   Wed, 11 Dec 2019 14:26:38 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, magnus.karlsson@...il.com,
        magnus.karlsson@...el.com, jonathan.lemon@...il.com,
        ecree@...arflare.com, thoiland@...hat.com, brouer@...hat.com,
        andrii.nakryiko@...il.com
Subject: Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher

[...]
> +/* 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/

-Toke