linux-kernel - [PATCH 2/2] drm/nouveau: WQ_PERCPU added to alloc

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Message-ID: <20251031102020.95349-3-marco.crivellari@suse.com>
Date: Fri, 31 Oct 2025 11:20:20 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	nouveau@...ts.freedesktop.org
Cc: Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Subject: [PATCH 2/2] drm/nouveau: 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 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’t explicitly specify WQ_UNBOUND
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 <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 drivers/gpu/drm/nouveau/nouveau_drm.c   | 2 +-
 drivers/gpu/drm/nouveau/nouveau_sched.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 1527b801f013..5a2970ef27d4 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -631,7 +631,7 @@ nouveau_drm_device_init(struct nouveau_drm *drm)
 	struct drm_device *dev = drm->dev;
 	int ret;

-	drm->sched_wq = alloc_workqueue("nouveau_sched_wq_shared", 0,
+	drm->sched_wq = alloc_workqueue("nouveau_sched_wq_shared", WQ_PERCPU,
 					WQ_MAX_ACTIVE);
 	if (!drm->sched_wq)
 		return -ENOMEM;
diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
index e60f7892f5ce..79cf157ab2a5 100644
--- a/drivers/gpu/drm/nouveau/nouveau_sched.c
+++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
@@ -416,7 +416,8 @@ nouveau_sched_init(struct nouveau_sched *sched, struct nouveau_drm *drm,
 	int ret;

 	if (!wq) {
-		wq = alloc_workqueue("nouveau_sched_wq_%d", 0, WQ_MAX_ACTIVE,
+		wq = alloc_workqueue("nouveau_sched_wq_%d", WQ_PERCPU,
+				     WQ_MAX_ACTIVE,
 				     current->pid);
 		if (!wq)
 			return -ENOMEM;
-- 
2.51.0