From: Martin K. Petersen Date: Thu, 13 Nov 2025 02:30:23 +0000 (-0500) Subject: Merge patch series "replace old wq(s), added WQ_PERCPU to alloc_workqueue" X-Git-Tag: v6.19-rc1~95^2~9 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e360bb6dc843ffa59283705dd167478ea317567c;p=thirdparty%2Flinux.git Merge patch series "replace old wq(s), added WQ_PERCPU to alloc_workqueue" Marco Crivellari says: Hi, === Current situation: problems === Let's consider a nohz_full system with isolated CPUs: wq_unbound_cpumask is set to the housekeeping CPUs, for !WQ_UNBOUND the local CPU is selected. This leads to different scenarios if a work item is scheduled on an isolated CPU where "delay" value is 0 or greater then 0: schedule_delayed_work(, 0); This will be handled by __queue_work() that will queue the work item on the current local (isolated) CPU, while: schedule_delayed_work(, 1); Will move the timer on an housekeeping CPU, and schedule the work there. 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 consistency cannot be addressed without refactoring the API. === Recent changes to the WQ API === The following, address the recent changes in the Workqueue API: - commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq") - commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag") The old workqueues will be removed in a future release cycle. === Introduced Changes by this series === 1) [P 1] Replace uses of system_wq and system_unbound_wq system_unbound_wq is to be used when locality is not required. Because of that, system_unbound_wq has been replaced with system_dfl_wq, to make clear it should be used when locality is not required. 2) [P 2-3-4] WQ_PERCPU added to alloc_workqueue() This change adds a new WQ_PERCPU flag to explicitly request alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified. Thanks! Link: https://patch.msgid.link/20251031095643.74246-1-marco.crivellari@suse.com Signed-off-by: Martin K. Petersen --- e360bb6dc843ffa59283705dd167478ea317567c