netdev - Re: [PATCH bpf-next] bpf: Add multi-prog support for XDP BPF programs

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Message-ID: <874j48rc13.fsf@toke.dk>
Date: Fri, 15 Nov 2024 12:07:04 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Ryan Wilson <ryantimwilson@...il.com>, Alexei Starovoitov
 <alexei.starovoitov@...il.com>
Cc: Network Development <netdev@...r.kernel.org>, Jakub Kicinski
 <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>, Alexei
 Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 ryantimwilson@...a.com, Willem de Bruijn
 <willemdebruijn.kernel@...il.com>, Jason Wang <jasowang@...hat.com>, Eric
 Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH bpf-next] bpf: Add multi-prog support for XDP BPF programs

Hi Ryan

I'll take a more detailed look at your patch later, but wanted to add
a few smallish comment now, see below:


Ryan Wilson <ryantimwilson@...il.com> writes:
> On Thu, Nov 14, 2024 at 4:52 PM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
>>
>> On Thu, Nov 14, 2024 at 9:07 AM Ryan Wilson <ryantimwilson@...il.com> wrote:
>> >
>> > Currently, network devices only support a single XDP program. However,
>> > there are use cases for multiple XDP programs per device. For example,
>> > at Meta, we have XDP programs for firewalls, DDOS and logging that must
>> > all run in a specific order. To work around the lack of multi-program
>> > support, a single daemon loads all programs and uses bpf_tail_call()
>> > in a loop to jump to each program contained in a BPF map.
>>
>> The support for multiple XDP progs per netdev is long overdue.
>> Thank you for working on this!

+1 on this!


[...]

> Note for real drivers, we do not hit this code. This is how it works
> for real drivers:
> - When installing a BPF program on a driver, we call the driver's
> ndo_bpf() callback function with command = XDP_QUERY_MPROG_SUPPORT. If
> this returns 0, then mprog is supported. Otherwise, mprog is not
> supported.

We already have feature flags for XDP, so why not just make mprog
support a feature flag instead of the query thing? It probably should be
anyway, so it can also be reported to userspace.

>> I think it will remove this branch and XDP performance will remain
>> the same ?
>> Benchmarking on real NIC matters, of course.
>
> Good point. I will migrate a real driver and add XDP benchmarking
> numbers to v2.

Yes, please, looking forward to seeing benchmark numbers!

-Toke