linux-kernel - Re: [PATCH] soc: fsl: qbman: add WQ_PERCPU to alloc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <64df8b4e-6cd4-49e4-a0f9-c8f9c017b06c@csgroup.eu>
Date: Sat, 8 Nov 2025 20:44:08 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Marco Crivellari <marco.crivellari@...e.com>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 Tejun Heo <tj@...nel.org>
Cc: Lai Jiangshan <jiangshanlai@...il.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Michal Hocko <mhocko@...e.com>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH] soc: fsl: qbman: add WQ_PERCPU to alloc_workqueue users



Le 07/11/2025 à 16:29, 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.
> 
> 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 a new WQ_PERCPU flag to explicitly request
> alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.
> 
> 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>

IIUC this patch is part of a wide work on workqueues. I assume the will 
go via the workqueue tree. Let me know if you want me to take it via soc 
fsl.

Acked-by: Christophe Leroy <christophe.leroy@...roup.eu>



> ---
>   drivers/soc/fsl/qbman/qman.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/fsl/qbman/qman.c b/drivers/soc/fsl/qbman/qman.c
> index 9be240999f87..6b392b3ad4b1 100644
> --- a/drivers/soc/fsl/qbman/qman.c
> +++ b/drivers/soc/fsl/qbman/qman.c
> @@ -1073,7 +1073,7 @@ EXPORT_SYMBOL(qman_portal_set_iperiod);
>   
>   int qman_wq_alloc(void)
>   {
> -	qm_portal_wq = alloc_workqueue("qman_portal_wq", 0, 1);
> +	qm_portal_wq = alloc_workqueue("qman_portal_wq", WQ_PERCPU, 1);
>   	if (!qm_portal_wq)
>   		return -ENOMEM;
>   	return 0;