linux-kernel - Re: [PATCH] drm/sched: replace use of system_wq with system_percpu

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Message-ID: <7808bc5fcac1236640f481733d1c8aaaf8accb02.camel@mailbox.org>
Date: Wed, 05 Nov 2025 09:39:46 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: Marco Crivellari <marco.crivellari@...e.com>, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Cc: 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>, Matthew Brost
 <matthew.brost@...el.com>, Danilo Krummrich <dakr@...nel.org>,  Philipp
 Stanner <phasta@...nel.org>, Christian Konig
 <ckoenig.leichtzumerken@...il.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH] drm/sched: replace use of system_wq with
 system_percpu_wq

nit: s/replace/Replace

On Tue, 2025-11-04 at 17:52 +0100, Marco Crivellari wrote:
> Currently if a user enqueue a work item using schedule_delayed_work() the

s/enqueue/enqueues

Also: maybe start the sentence with something like "In the general
workqueue implementation, if a user […]". Otherwise it at first reads
as if we're talking about a drm/sched user here.

In general, the commit message should focus more on drm/sched. See
below, too.

> used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
> WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
> schedule_work() that is using system_wq and queue_work(), that makes use
> again of WORK_CPU_UNBOUND.
> 
> This lack of consistentcy cannot be addressed without refactoring the API.
> 
> This patch continues the effort to refactor worqueue APIs, which has begun
> with the change introducing new workqueues and a new alloc_workqueue flag:
> 
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

>From my POV it would be enough if you provide these commits in this
commit message and maybe a Link: to the overall discussion in the
workqueue subsystem / implementation.

You can give the details above if you want, but I think drm/sched
doesn't care too much about them. The drm/sched users who really care
about the timeout_wq's exact behavior use one they allocate themselves
anyways.

> 
> system_wq should be the per-cpu workqueue, yet in this name nothing makes
> that clear, so replace system_wq with system_percpu_wq.
> 
> The old wq (system_wq) will be kept for a few release cycles.

Please state in your commit message what you're actually doing to
drm/sched. Like:

"Use the successor of system_wq, system_percpu_wq, for the scheduler's
default timeout_wq. system_wq will be removed in a few release cycles."

> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
>  drivers/gpu/drm/scheduler/sched_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index c39f0245e3a9..13192e99637a 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -1315,7 +1315,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched, const struct drm_sched_init_
>  	sched->name = args->name;
>  	sched->timeout = args->timeout;
>  	sched->hang_limit = args->hang_limit;
> -	sched->timeout_wq = args->timeout_wq ? args->timeout_wq : system_wq;
> +	sched->timeout_wq = args->timeout_wq ? args->timeout_wq : system_percpu_wq;

Actual change looks fine by me.


Thanks for your patch,
P.

>  	sched->score = args->score ? args->score : &sched->_score;
>  	sched->dev = args->dev;
>