linux-kernel - Re: [PATCH v2] smp: replace use of system_wq with system_percpu

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Message-ID: <aYN45Ah1J47Y8XWw@2a01cb06901b87bf2e33c71cd27c366b.ipv6.abo.wanadoo.fr>
Date: Wed, 4 Feb 2026 17:50:44 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Marco Crivellari <marco.crivellari@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Michal Hocko <mhocko@...e.com>, Ingo Molnar <mingo@...hat.com>,
	Rik van Riel <riel@...riel.com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] smp: replace use of system_wq with system_percpu_wq

Le Mon, Nov 10, 2025 at 06:03:32PM +0100, Marco Crivellari a écrit :
> 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 continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
> 
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> 
> Switch to using system_percpu_wq because system_wq is going away as part of
> a workqueue restructuring.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
> Changes in v2:
> - improved commit log
> - rebased on 6.18-rc5
> ---
>  kernel/smp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 02f52291fae4..496358eae37c 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -1137,7 +1137,7 @@ int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys)
>  	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
>  		return -ENXIO;
>  
> -	queue_work_on(cpu, system_wq, &sscs.work);
> +	queue_work_on(cpu, system_percpu_wq, &sscs.work);

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>

-- 
Frederic Weisbecker
SUSE Labs