linux-kernel - [PATCH 1/3] drm/atomic-helper: replace use of system_unbound_wq with system_dfl

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Message-ID: <20251030162043.292468-2-marco.crivellari@suse.com>
Date: Thu, 30 Oct 2025 17:20:41 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	dri-devel@...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>,
	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 1/3] drm/atomic-helper: replace use of system_unbound_wq with system_dfl_wq

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.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index d5ebe6ea0acb..166085a7e681 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2222,13 +2222,13 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 	 * current layout.
 	 *
 	 * NOTE: Commit work has multiple phases, first hardware commit, then
-	 * cleanup. We want them to overlap, hence need system_unbound_wq to
+	 * cleanup. We want them to overlap, hence need system_dfl_wq to
 	 * make sure work items don't artificially stall on each another.
 	 */
 
 	drm_atomic_state_get(state);
 	if (nonblock)
-		queue_work(system_unbound_wq, &state->commit_work);
+		queue_work(system_dfl_wq, &state->commit_work);
 	else
 		commit_tail(state);
 
@@ -2261,7 +2261,7 @@ EXPORT_SYMBOL(drm_atomic_helper_commit);
  *
  * Asynchronous workers need to have sufficient parallelism to be able to run
  * different atomic commits on different CRTCs in parallel. The simplest way to
- * achieve this is by running them on the &system_unbound_wq work queue. Note
+ * achieve this is by running them on the &system_dfl_wq work queue. Note
  * that drivers are not required to split up atomic commits and run an
  * individual commit in parallel - userspace is supposed to do that if it cares.
  * But it might be beneficial to do that for modesets, since those necessarily
-- 
2.51.0