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Tsirkin" , David Hildenbrand , Jason Wang , Xuan Zhuo , Eugenio Perez Subject: [PATCH 2/2] vduse: add WQ_PERCPU to alloc_workqueue users Date: Fri, 7 Nov 2025 16:49:17 +0100 Message-ID: <20251107154917.313090-3-marco.crivellari@suse.com> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251107154917.313090-1-marco.crivellari@suse.com> References: <20251107154917.313090-1-marco.crivellari@suse.com> 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/vdpa/vdpa_user/vduse_dev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vd= use_dev.c index e7bced0b5542..ae357d014564 100644 --- a/drivers/vdpa/vdpa_user/vduse_dev.c +++ b/drivers/vdpa/vdpa_user/vduse_dev.c @@ -2173,7 +2173,8 @@ static int vduse_init(void) if (!vduse_irq_wq) goto err_wq; =20 - vduse_irq_bound_wq =3D alloc_workqueue("vduse-irq-bound", WQ_HIGHPRI, 0); + vduse_irq_bound_wq =3D alloc_workqueue("vduse-irq-bound", + WQ_HIGHPRI | WQ_PERCPU, 0); if (!vduse_irq_bound_wq) goto err_bound_wq; =20 --=20 2.51.1