linux-kernel - Re: [PATCH bpf-next v3 1/3] xsk: Support UMEM chunk_size > PAGE

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Message-ID: <87o7nmwul7.fsf@toke.dk>
Date:   Mon, 17 Apr 2023 14:40:04 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Magnus Karlsson <magnus.karlsson@...il.com>
Cc:     Kal Cutter Conley <kal.conley@...tris.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 1/3] xsk: Support UMEM chunk_size > PAGE_SIZE

Magnus Karlsson <magnus.karlsson@...il.com> writes:

> On Thu, 13 Apr 2023 at 22:52, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Kal Cutter Conley <kal.conley@...tris.com> writes:
>>
>> >> Well, you mentioned yourself that:
>> >>
>> >> > The disadvantage of this patchset is requiring the user to allocate
>> >> > HugeTLB pages which is an extra complication.
>> >
>> > It's a small extra complication *for the user*. However, users that
>> > need this feature are willing to allocate hugepages. We are one such
>> > user. For us, having to deal with packets split into disjoint buffers
>> > (from the XDP multi-buffer paradigm) is a significantly more annoying
>> > complication than allocating hugepages (particularly on the RX side).
>>
>> "More annoying" is not a great argument, though. You're basically saying
>> "please complicate your code so I don't have to complicate mine". And
>> since kernel API is essentially frozen forever, adding more of them
>> carries a pretty high cost, which is why kernel developers tend not to
>> be easily swayed by convenience arguments (if all you want is a more
>> convenient API, just build one on top of the kernel primitives and wrap
>> it into a library).
>>
>> So you'll need to come up with either (1) a use case that you *can't*
>> solve without this new API (with specifics as to why that is the case),
>> or (2) a compelling performance benchmark showing the complexity is
>> worth it. Magnus indicated he would be able to produce the latter, in
>> which case I'm happy to be persuaded by the numbers.
>
> We will measure it and get back to you. Would be good with some
> numbers.

Sounds good, thanks! :)

-Toke