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Fri, 07 Nov 2025 07:37:46 -0800 (PST) Received: from localhost.localdomain ([2a00:6d43:105:c401:e307:1a37:2e76:ce91]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42ac67845ccsm5763460f8f.36.2025.11.07.07.37.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Nov 2025 07:37:45 -0800 (PST) From: Marco Crivellari To: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Frederic Weisbecker , Sebastian Andrzej Siewior , Marco Crivellari , Michal Hocko , Greg Kroah-Hartman Subject: [PATCH 1/2] USB: add WQ_PERCPU to alloc_workqueue users Date: Fri, 7 Nov 2025 16:37:30 +0100 Message-ID: <20251107153737.301413-2-marco.crivellari@suse.com> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251107153737.301413-1-marco.crivellari@suse.com> References: <20251107153737.301413-1-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/usb/core/hub.c | 2 +- drivers/usb/gadget/function/f_hid.c | 3 +-- 2 files changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index 256fe8c86828..b5cbcdb08a5d 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -6077,7 +6077,7 @@ int usb_hub_init(void) * device was gone before the EHCI controller had handed its port * over to the companion full-speed controller. */ - hub_wq =3D alloc_workqueue("usb_hub_wq", WQ_FREEZABLE, 0); + hub_wq =3D alloc_workqueue("usb_hub_wq", WQ_FREEZABLE | WQ_PERCPU, 0); if (hub_wq) return 0; =20 diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/funct= ion/f_hid.c index 307ea563af95..3ddfd4f66f0b 100644 --- a/drivers/usb/gadget/function/f_hid.c +++ b/drivers/usb/gadget/function/f_hid.c @@ -1272,8 +1272,7 @@ static int hidg_bind(struct usb_configuration *c, str= uct usb_function *f) =20 INIT_WORK(&hidg->work, get_report_workqueue_handler); hidg->workqueue =3D alloc_workqueue("report_work", - WQ_FREEZABLE | - WQ_MEM_RECLAIM, + WQ_FREEZABLE | WQ_MEM_RECLAIM | WQ_PERCPU, 1); =20 if (!hidg->workqueue) { --=20 2.51.1