From: Marco Crivellari Date: Fri, 5 Sep 2025 09:05:33 +0000 (+0200) Subject: padata: WQ_PERCPU added to alloc_workqueue users X-Git-Tag: v6.18-rc1~84^2~17 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4fcd322914068f2c6aec7bb5cfd12ce0207b3a21;p=thirdparty%2Fkernel%2Fstable.git padata: WQ_PERCPU added to alloc_workqueue users Currently if a user enqueue 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 consistentcy 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 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 patch adds a new WQ_PERCPU flag to explicitly request the use of the per-CPU behavior. Both flags coexist for one release cycle to allow callers to transition their calls. Once migration is complete, WQ_UNBOUND can be removed and unbound will become the implicit default. 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. All existing users have been updated accordingly. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari Signed-off-by: Herbert Xu --- diff --git a/kernel/padata.c b/kernel/padata.c index d7cc95367209b..f4def028c48c0 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -967,8 +967,9 @@ struct padata_instance *padata_alloc(const char *name) cpus_read_lock(); - pinst->serial_wq = alloc_workqueue("%s_serial", WQ_MEM_RECLAIM | - WQ_CPU_INTENSIVE, 1, name); + pinst->serial_wq = alloc_workqueue("%s_serial", + WQ_MEM_RECLAIM | WQ_CPU_INTENSIVE | WQ_PERCPU, + 1, name); if (!pinst->serial_wq) goto err_put_cpus;