netdev - Re: [PATCH bpf-next v8 2/5] Documentation/bpf: Add documentation for BPF_PROG

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Message-ID: <20220302190440.t5cvezlkg7ynajam@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 2 Mar 2022 11:04:40 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v8 2/5] Documentation/bpf: Add documentation for
 BPF_PROG_RUN

On Fri, Feb 18, 2022 at 06:50:26PM +0100, Toke Høiland-Jørgensen wrote:
> This adds documentation for the BPF_PROG_RUN command; a short overview of
> the command itself, and a more verbose description of the "live packet"
> mode for XDP introduced in the previous commit.

Overall the patch set looks great. The doc really helps.
One nit below.

> +- When running the program with multiple repetitions, the execution will happen
> +  in batches, where the program is executed multiple times in a loop, the result
> +  is saved, and other actions (like redirecting the packet or passing it to the
> +  networking stack) will happen for the whole batch after the execution. This is
> +  similar to how execution happens in driver-mode XDP for each hardware NAPI
> +  cycle. The batch size defaults to 64 packets (which is same as the NAPI batch
> +  size), but the batch size can be specified by userspace through the
> +  ``batch_size`` parameter, up to a maximum of 256 packets.

This paragraph is a bit confusing.
I've read it as the program can do only one kind of result per batch and
it will apply to the whole batch.
But the program can do XDP_PASS/REDIRECT in any order.
Can you make "the result is saved" a bit more clear?