netdev - RE: [PATCH bpf-next 0/8] Add support for transmitting packets using XDP in bpf_prog

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Message-ID: <871r2lydga.fsf@toke.dk>
Date:   Thu, 09 Dec 2021 17:01:41 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>,
        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>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: RE: [PATCH bpf-next 0/8] Add support for transmitting packets using
 XDP in bpf_prog_run()

John Fastabend <john.fastabend@...il.com> writes:

> Toke Høiland-Jørgensen wrote:
>> This series adds support for transmitting packets using XDP in
>> bpf_prog_run(), by enabling the xdp_do_redirect() callback so XDP programs
>> can perform "real" redirects to devices or maps, using an opt-in flag when
>> executing the program.
>> 
>> The primary use case for this is testing the redirect map types and the
>> ndo_xdp_xmit driver operation without generating external traffic. But it
>> turns out to also be useful for creating a programmable traffic generator.
>> The last patch adds a sample traffic generator to bpf/samples, which
>> can transmit up to 11.5 Mpps/core on my test machine.
>> 
>> To transmit the frames, the new mode instantiates a page_pool structure in
>> bpf_prog_run() and initialises the pages with the data passed in by
>> userspace. These pages can then be redirected using the normal redirection
>> mechanism, and the existing page_pool code takes care of returning and
>> recycling them. The setup is optimised for high performance with a high
>> number of repetitions to support stress testing and the traffic generator
>> use case; see patch 6 for details.
>> 
>> The series is structured as follows: Patches 1-2 adds a few features to
>> page_pool that are needed for the usage in bpf_prog_run(). Similarly,
>> patches 3-5 performs a couple of preparatory refactorings of the XDP
>> redirect and memory management code. Patch 6 adds the support to
>> bpf_prog_run() itself, patch 7 adds a selftest, and patch 8 adds the
>> traffic generator example to samples/bpf.
>
> Overall looks pretty good. Couple questions in the series though.

Yay! Thank you for the review! Will reply to each of those...

-Toke