linux-kernel - [PATCH v2 0/2] replace system_unbound_wq and system

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Message-ID: <20251029165642.364488-1-marco.crivellari@suse.com>
Date: Wed, 29 Oct 2025 17:56:40 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: 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>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Maciej Falkowski <maciej.falkowski@...ux.intel.com>,
	Karol Wachowski <karol.wachowski@...ux.intel.com>,
	Oded Gabbay <ogabbay@...nel.org>
Subject: [PATCH v2 0/2] replace system_unbound_wq and system_wq with the new wqs

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] 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.


Thanks!

---
Changes in v2:
- Fixed warning about length of lines

- Fixed typo in the cover letter

Marco Crivellari (2):
  accel/ivpu: replace use of system_unbound_wq with system_dfl_wq
  accel/ivpu: replace use of system_wq with system_percpu_wq

 drivers/accel/ivpu/ivpu_hw_btrs.c | 2 +-
 drivers/accel/ivpu/ivpu_ipc.c     | 2 +-
 drivers/accel/ivpu/ivpu_job.c     | 2 +-
 drivers/accel/ivpu/ivpu_mmu.c     | 2 +-
 drivers/accel/ivpu/ivpu_pm.c      | 5 +++--
 5 files changed, 7 insertions(+), 6 deletions(-)

-- 
2.51.0