linux-kernel - Re: [PATCH 0/3] replace system_unbound_wq and system

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Message-ID: <a68bac38-ac0e-4ad6-8b70-72b09811a21e@suse.de>
Date: Wed, 4 Feb 2026 12:58:40 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
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>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH 0/3] replace system_unbound_wq and system_wq with the new
 wqs

Hi

Am 30.10.25 um 17:20 schrieb Marco Crivellari:
> Hi,
>
> === Current situation: problems ===
>
> Let's consider a nohz_full system with isolated CPUs: wq_unbound_cpumask is
> set to the housekeeping CPUs, for !WQ_UNBOUND the local CPU is selected.
>
> This leads to different scenarios if a work item is scheduled on an
> isolated CPU where "delay" value is 0 or greater then 0:
>          schedule_delayed_work(, 0);
>
> This will be handled by __queue_work() that will queue the work item on the
> current local (isolated) CPU, while:
>
>          schedule_delayed_work(, 1);
>
> Will move the timer on an housekeeping CPU, and schedule the work there.
>
> Currently if a user enqueue a work item using schedule_delayed_work() the
> 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 consistency cannot be addressed without refactoring the API.
>
> === Recent changes to the WQ API ===
>
> The following, address the recent changes in the Workqueue API:
>
> - commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> - commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
>
> The old workqueues will be removed in a future release cycle.
>
> === Introduced Changes by this series ===
>
> 1) [P 1-2-3]  Replace uses of system_wq and system_unbound_wq
>
>      system_wq is a per-CPU workqueue, but his name is not clear.
>      system_unbound_wq is to be used when locality is not required.
>
>      Because of that, system_wq has been replaced with system_percpu_wq, and
>      system_unbound_wq has been replaced with system_dfl_wq.

 From the description, I've found it hard to see if there's a change in 
semantics here. But this series is effectively about renaming AFAICT. If so,

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

for all patches.

Best regards
Thomas

>
> Thanks!
>
>
> Marco Crivellari (3):
>    drm/atomic-helper: replace use of system_unbound_wq with system_dfl_wq
>    drm/probe-helper: replace use of system_wq with system_percpu_wq
>    drm/self_refresh: replace use of system_wq with system_percpu_wq
>
>   drivers/gpu/drm/drm_atomic_helper.c       | 6 +++---
>   drivers/gpu/drm/drm_probe_helper.c        | 2 +-
>   drivers/gpu/drm/drm_self_refresh_helper.c | 2 +-
>   3 files changed, 5 insertions(+), 5 deletions(-)
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)