linux-kernel - Re: [PATCH v2] tracing: Replace use of system_wq with system_dfl

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Message-ID: <20251230094236.358ae2d8@gandalf.local.home>
Date: Tue, 30 Dec 2025 09:42:36 -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 v2] tracing: Replace use of system_wq with system_dfl_wq

On Tue, 30 Dec 2025 15:28:20 +0100
Marco Crivellari <marco.crivellari@...e.com> wrote:

> This patch continues the effort to refactor workqueue APIs, which has begun
> with the changes 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")
> 
> The point of the refactoring is to eventually alter the default behavior of
> workqueues to become unbound by default so that their workload placement is
> optimized by the scheduler.
> 
> 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 specific workflow has no benefits being per-cpu, so instead of
> system_percpu_wq the new unbound workqueue has been used (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>
> ---
> Changes in v2:
> - use system_dfl_wq instead of system_percpu_wq because this workload has no
>   benefits being per-cpu.

Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve