linux-kernel - Re: [PATCH] iio/adc/pac1934: replace use of system_wq with system_percpu

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Message-ID: <20251109164536.2ed7867d@jic23-huawei>
Date: Sun, 9 Nov 2025 16:45:36 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-iio@...r.kernel.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>, Marius Cristea
 <marius.cristea@...rochip.com>
Subject: Re: [PATCH] iio/adc/pac1934: replace use of system_wq with
 system_percpu_wq

On Wed,  5 Nov 2025 11:43:30 +0100
Marco Crivellari <marco.crivellari@...e.com> wrote:

> Currently if a user enqueues 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.
> 
> 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")
> 
> system_percpu_wq replaced system_wq, so change the wq in iio/adc/pac1934.
> 
> The old wq (system_wq) will be kept for a few release cycles.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
I'd start these descriptions off by saying the system_wq is deprecated.
Then people are already on the page for there being a necessity to make
a change.

Anyhow, I've seen enough of the discussion of other related patches to
be fine with this.

Applied.

> ---
>  drivers/iio/adc/pac1934.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/pac1934.c b/drivers/iio/adc/pac1934.c
> index 48df16509260..ec96bb0f2ed6 100644
> --- a/drivers/iio/adc/pac1934.c
> +++ b/drivers/iio/adc/pac1934.c
> @@ -768,7 +768,7 @@ static int pac1934_retrieve_data(struct pac1934_chip_info *info,
>  		 * Re-schedule the work for the read registers on timeout
>  		 * (to prevent chip registers saturation)
>  		 */
> -		mod_delayed_work(system_wq, &info->work_chip_rfsh,
> +		mod_delayed_work(system_percpu_wq, &info->work_chip_rfsh,
>  				 msecs_to_jiffies(PAC1934_MAX_RFSH_LIMIT_MS));
>  	}
>