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Fri, 07 Nov 2025 06:36:32 -0800 (PST) Received: from localhost.localdomain ([2a00:6d43:105:c401:e307:1a37:2e76:ce91]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4776bd08834sm52478435e9.15.2025.11.07.06.36.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Nov 2025 06:36:32 -0800 (PST) From: Marco Crivellari To: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Frederic Weisbecker , Sebastian Andrzej Siewior , Marco Crivellari , Michal Hocko , Bjorn Helgaas , Ilpo Jarvinen Subject: [PATCH] PCI: shpchp: add WQ_PERCPU to alloc_workqueue users Date: Fri, 7 Nov 2025 15:36:24 +0100 Message-ID: <20251107143624.244978-1-marco.crivellari@suse.com> X-Mailer: git-send-email 2.51.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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=E2=80=99re 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=E2=80=99t explicitly specify WQ_UNB= OUND 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 Signed-off-by: Marco Crivellari --- drivers/pci/hotplug/shpchp_core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/pci/hotplug/shpchp_core.c b/drivers/pci/hotplug/shpchp= _core.c index 0c341453afc6..56308515ecba 100644 --- a/drivers/pci/hotplug/shpchp_core.c +++ b/drivers/pci/hotplug/shpchp_core.c @@ -80,7 +80,8 @@ static int init_slots(struct controller *ctrl) slot->device =3D ctrl->slot_device_offset + i; slot->number =3D ctrl->first_slot + (ctrl->slot_num_inc * i); =20 - slot->wq =3D alloc_workqueue("shpchp-%d", 0, 0, slot->number); + slot->wq =3D alloc_workqueue("shpchp-%d", WQ_PERCPU, 0, + slot->number); if (!slot->wq) { retval =3D -ENOMEM; goto error_slot; --=20 2.51.1