linux-kernel - Re: [PATCH RFC bpf-next 0/9] allow HID-BPF to do device IOs

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Message-ID: <87bk8pve2z.fsf@toke.dk>
Date: Fri, 09 Feb 2024 16:42:44 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
 <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, Martin
 KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Jiri Kosina
 <jikos@...nel.org>, Benjamin Tissoires <benjamin.tissoires@...hat.com>,
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Benjamin Tissoires <bentiss@...nel.org>
Subject: Re: [PATCH RFC bpf-next 0/9] allow HID-BPF to do device IOs

Benjamin Tissoires <bentiss@...nel.org> writes:

> [Putting this as a RFC because I'm pretty sure I'm not doing the things
> correctly at the BPF level.]
> [Also using bpf-next as the base tree as there will be conflicting
> changes otherwise]
>
> Ideally I'd like to have something similar to bpf_timers, but not
> in soft IRQ context. So I'm emulating this with a sleepable
> bpf_tail_call() (see "HID: bpf: allow to defer work in a delayed
> workqueue").

Why implement a new mechanism? Sounds like what you need is essentially
the bpf_timer functionality, just running in a different context, right?
So why not just add a flag to the timer setup that controls the callback
context? I've been toying with something similar for restarting XDP TX
for my queueing patch series (though I'm not sure if this will actually
end up being needed in the end):

https://git.kernel.org/pub/scm/linux/kernel/git/toke/linux.git/commit/?h=xdp-queueing-08&id=54bc201a358d1ac6ebfe900099315bbd0a76e862

-Toke