linux-kernel - Re: [PATCH] media: platform: mtk-mdp3: add WQ_PERCPU to alloc

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Message-ID: <CAAofZF44pUoyDPnnv9UUuMkYvqiSWP4gELg4rutgo=3tNpBZsw@mail.gmail.com>
Date: Wed, 10 Dec 2025 16:30:15 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: Nicolas Dufresne <nicolas@...fresne.ca>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Michal Hocko <mhocko@...e.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH] media: platform: mtk-mdp3: add WQ_PERCPU to
 alloc_workqueue users

On Tue, Dec 9, 2025 at 9:57 PM Nicolas Dufresne <nicolas@...fresne.ca> wrote:
>
> Hi,
> I have to admit, there is likely no review here due to the lack of knowledge, so
> in order to help educate myself (hopefully its not just me), can you explain why
> the new default of WQ_UNBOUND would not be a fit for this driver ? After all,
> the author didn't care and didn't make a choice, so I feel like its worth
> asking.

Hi Nicolas,

The fact is that "alloc_workqueue()" without WQ_UNBOUND it means per-cpu.
So what we are doing here is just make explicit that the workqueue is per-cpu.

Currently there are no behavioral changes in alloc_workqueue(); in a
future release
WQ_UNBOUND will be removed and unbound will be the default. But as for now,
it is still per-cpu.

We can of course change the current behavior and I can send the v2 with
WQ_UNBOUND instead. Looking at the code there are not per-cpu variable and
the workqueue does not have the WQ_BH flag, so we can convert it if it
is better.

Thanks!

--

Marco Crivellari

L3 Support Engineer