linux-kernel - Re: [PATCH bpf-next 17/18] bpf: add bpf_wq

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Date: Fri, 19 Apr 2024 18:01:28 +0200
From: Benjamin Tissoires <bentiss@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, 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>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next 17/18] bpf: add bpf_wq_start

On Apr 19 2024, Alexei Starovoitov wrote:
> On Fri, Apr 19, 2024 at 8:14 AM Benjamin Tissoires <bentiss@...nel.org> wrote:
> >
> >
> > Honestly I just felt the patch series was big enough for a PoC and
> > comparison with sleepable bpf_timer. But if we think this needs not to
> > be added, I guess that works too :)
> 
> It certainly did its job to compare the two and imo bpf_wq with kfunc approach
> looks cleaner overall and will be easier to extend in the long term.

Yeah. I agree. I'm also glad we pick the bpf_wq approach as I gave it a
lot more care :)

Talking about extending, I think I'll need delayed_work soon enough.
Most of the time when I receive an input event, the device is preventing
any communication with it, and with plain bpf_wq, it's likely that when
the code kicks in the device won't have processed the current input,
meaning to a useless retry. With delayed_works, I can schedule it
slightly later, and have a higher chance of not having to retry.

I've got a quick hack locally that I can submit once this series get
merged.

> 
> I mean that we'll be adding 3 kfuncs initially:
> bpf_wq_init, bpf_wq_start, bpf_wq_set_callback.
> 
> imo that's good enough to land it and get some exposure.

sounds good to me.

> I'll be using it right away to refactor bpf_arena_alloc.h into
> actual arena allocator for bpf progs that is not just a selftest.
> 
> I'm currently working on locks for bpf_arena.
> Kumar has a patch set that adds bpf_preempt_disble kfunc and
> coupled with bpf_wq we'll have all mechanisms to build
> arbitrary data structures/algorithms as bpf programs.

Oh. I did not realize that it was that needed for outside of my
playground. That's good to hear :)

Cheers,
Benjamin