linux-kernel - Re: [PATCH] tracing: Replace use of system_wq with system_percpu

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Message-ID: <20251224133210.7b62ba5e@gandalf.local.home>
Date: Wed, 24 Dec 2025 15:44:59 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...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>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Replace use of system_wq with system_percpu_wq

On Wed, 24 Dec 2025 17:20:00 +0100
Marco Crivellari <marco.crivellari@...e.com> wrote:

> Before that to happen after a careful review and conversion of each individual
> case, workqueue users must be converted to the better named new workqueues with
> no intended behaviour changes:
> 
>    system_wq -> system_percpu_wq
>    system_unbound_wq -> system_dfl_wq
> 
> This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
> removed in the future.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
>  kernel/trace/trace_events_filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 385af8405392..bb6de1d38f78 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -1375,7 +1375,7 @@ static void free_filter_list_tasks(struct rcu_head *rhp)
>  	struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu);
>  
>  	INIT_RCU_WORK(&filter_list->rwork, free_filter_list_work);
> -	queue_rcu_work(system_wq, &filter_list->rwork);
> +	queue_rcu_work(system_percpu_wq, &filter_list->rwork);

This is just garbage collection and has no need to be done on the CPU it
was queued on. I guess this can use system_dfl_wq?

-- Steve


>  }
>