[Intel-gfx] [PATCH] drm/i915: Queue page flip work with high priority

[Imre Deak]

While user space has control over the scheduling priority of its page
flipping thread, the corresponding work the driver schedules for MMIO
flips always runs with normal scheduling priority. This would hinder an
application that wants more stringent guarantees over flip timing (to
avoid missing a flip at the next frame count).

Fix this by scheduling the work with high priority, meaning normal
scheduling policy with -20 nice level.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97775
Testcase: igt/kms_cursor_legacy
CC: Chris Wilson <chris at chris-wilson.co.uk>
CC: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c      | 7 +++++++
 drivers/gpu/drm/i915/i915_drv.h      | 4 ++++
 drivers/gpu/drm/i915/intel_display.c | 2 +-
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 02c34d6..381ef23 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -756,8 +756,14 @@ static int i915_workqueues_init(struct drm_i915_private *dev_priv)
 	if (dev_priv->hotplug.dp_wq == NULL)
 		goto out_free_wq;
 
+	dev_priv->flip_wq = alloc_workqueue("i915-flip", WQ_HIGHPRI, 0);
+	if (dev_priv->flip_wq == NULL)
+		goto out_free_dp_wq;
+
 	return 0;
 
+out_free_dp_wq:
+	destroy_workqueue(dev_priv->hotplug.dp_wq);
 out_free_wq:
 	destroy_workqueue(dev_priv->wq);
 out_err:
@@ -768,6 +774,7 @@ out_err:
 
 static void i915_workqueues_cleanup(struct drm_i915_private *dev_priv)
 {
+	destroy_workqueue(dev_priv->flip_wq);
 	destroy_workqueue(dev_priv->hotplug.dp_wq);
 	destroy_workqueue(dev_priv->wq);
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f499fa5..3653ce4 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1844,6 +1844,10 @@ struct drm_i915_private {
 	 * result in deadlocks.
 	 */
 	struct workqueue_struct *wq;
+	/**
+	 * flip_wq - High priority flip workqueue.
+	 */
+	struct workqueue_struct *flip_wq;
 
 	/* Display functions */
 	struct drm_i915_display_funcs display;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3c367d0..48433e1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12278,7 +12278,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 
 		work->flip_queued_req = i915_gem_active_get(&obj->last_write,
 							    &obj->base.dev->struct_mutex);
-		schedule_work(&work->mmio_work);
+		queue_work(dev_priv->flip_wq, &work->mmio_work);
 	} else {
 		request = i915_gem_request_alloc(engine, engine->last_context);
 		if (IS_ERR(request)) {
-- 
2.5.0