linux-kernel - [PATCH 3/3] drm/i915: WQ_PERCPU added to alloc

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Message-ID: <20251031100923.85721-4-marco.crivellari@suse.com>
Date: Fri, 31 Oct 2025 11:09:23 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	intel-gfx@...ts.freedesktop.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>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Subject: [PATCH 3/3] drm/i915: 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/i915/display/intel_display_driver.c | 4 ++--
 drivers/gpu/drm/i915/i915_driver.c                  | 3 ++-
 drivers/gpu/drm/i915/selftests/i915_sw_fence.c      | 2 +-
 drivers/gpu/drm/i915/selftests/mock_gem_device.c    | 2 +-
 4 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_driver.c b/drivers/gpu/drm/i915/display/intel_display_driver.c
index cf1c14412abe..e12f9126b155 100644
--- a/drivers/gpu/drm/i915/display/intel_display_driver.c
+++ b/drivers/gpu/drm/i915/display/intel_display_driver.c
@@ -257,13 +257,13 @@ int intel_display_driver_probe_noirq(struct intel_display *display)
 		goto cleanup_wq_modeset;
 	}
 
-	display->wq.cleanup = alloc_workqueue("i915_cleanup", WQ_HIGHPRI, 0);
+	display->wq.cleanup = alloc_workqueue("i915_cleanup", WQ_HIGHPRI | WQ_PERCPU, 0);
 	if (!display->wq.cleanup) {
 		ret = -ENOMEM;
 		goto cleanup_wq_flip;
 	}
 
-	display->wq.unordered = alloc_workqueue("display_unordered", 0, 0);
+	display->wq.unordered = alloc_workqueue("display_unordered", WQ_PERCPU, 0);
 	if (!display->wq.unordered) {
 		ret = -ENOMEM;
 		goto cleanup_wq_cleanup;
diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
index 0f33cdc11736..380cb20a47c6 100644
--- a/drivers/gpu/drm/i915/i915_driver.c
+++ b/drivers/gpu/drm/i915/i915_driver.c
@@ -143,7 +143,8 @@ static int i915_workqueues_init(struct drm_i915_private *dev_priv)
 	 * to be scheduled on the system_percpu_wq before moving to a driver
 	 * instance due deprecation of flush_scheduled_work().
 	 */
-	dev_priv->unordered_wq = alloc_workqueue("i915-unordered", 0, 0);
+	dev_priv->unordered_wq = alloc_workqueue("i915-unordered", WQ_PERCPU,
+						 0);
 	if (dev_priv->unordered_wq == NULL)
 		goto out_free_wq;
 
diff --git a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
index 8f5ce71fa453..b81d65c77458 100644
--- a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
+++ b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
@@ -526,7 +526,7 @@ static int test_ipc(void *arg)
 	struct workqueue_struct *wq;
 	int ret = 0;
 
-	wq = alloc_workqueue("i1915-selftest", 0, 0);
+	wq = alloc_workqueue("i1915-selftest", WQ_PERCPU, 0);
 	if (wq == NULL)
 		return -ENOMEM;
 
diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
index fb8751bd5df0..684e6ca0f960 100644
--- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c
+++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c
@@ -221,7 +221,7 @@ struct drm_i915_private *mock_gem_device(void)
 	if (!i915->wq)
 		goto err_drv;
 
-	i915->unordered_wq = alloc_workqueue("mock-unordered", 0, 0);
+	i915->unordered_wq = alloc_workqueue("mock-unordered", WQ_PERCPU, 0);
 	if (!i915->unordered_wq)
 		goto err_wq;
 
-- 
2.51.0