linux-kernel - Re: [PATCH v2] firewire: core: add WQ_UNBOUND to alloc

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Message-ID: <20251112125600.GA325192@workstation.local>
Date: Wed, 12 Nov 2025 21:56:00 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, linux1394-devel@...ts.sourceforge.net,
	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>
Subject: Re: [PATCH v2] firewire: core: add WQ_UNBOUND to alloc_workqueue
 users

Hi,

On Wed, Nov 12, 2025 at 01:01:25PM +0100, Marco Crivellari 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.
> 
> alloc_workqueue() treats all queues as per-CPU by default, while unbound
> workqueues must opt-in via WQ_UNBOUND.
> 
> This default is suboptimal: most workloads benefit from unbound queues,
> allowing the scheduler to place worker threads where they’re needed and
> reducing noise when CPUs are isolated.
> 
> 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")
> 
> This change adds the WQ_UNBOUND flag to explicitly request
> alloc_workqueue() to be unbound, because this specific workload has no
> benefit being per-cpu.
> 
> With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> must now use WQ_PERCPU.
> 
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
> Changes in v2:
> - This workload benefit from an unbound workqueue. So change WQ_PERCPU
>   with WQ_UNBOUND_WQ.
> 
> - Rebased on 6.18-rc5
> ---
>  drivers/firewire/core-transaction.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Applied to for-next branch.

I'm sorry not to reply to your previous post since it did not reach my
mail box... Your v2 patch is a good reminder ;)


Thanks

Takashi Sakamoto