linux-kernel - [PATCH 2/3] drm/atomic: Use kthread worker for nonblocking commits

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Message-Id: <20200919193727.2093945-3-robdclark@gmail.com>
Date:   Sat, 19 Sep 2020 12:37:25 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
        timmurray@...gle.com, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 2/3] drm/atomic: Use kthread worker for nonblocking commits

From: Rob Clark <robdclark@...omium.org>

This will allow us to more easily switch scheduling rules based on what
userspace wants.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/drm_atomic_helper.c | 13 ++++++++----
 include/drm/drm_atomic.h            | 31 +++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 9e1ad493e689..75eeec5e7b10 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1659,11 +1659,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
 	drm_atomic_state_put(old_state);
 }
 
-static void commit_work(struct work_struct *work)
+static void commit_work(struct kthread_work *work)
 {
 	struct drm_atomic_state *state = container_of(work,
 						      struct drm_atomic_state,
-						      commit_work);
+						      commit_kwork);
 	commit_tail(state);
 }
 
@@ -1797,6 +1797,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 			     struct drm_atomic_state *state,
 			     bool nonblock)
 {
+	struct kthread_worker *worker = NULL;
 	int ret;
 
 	if (state->async_update) {
@@ -1814,7 +1815,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 	if (ret)
 		return ret;
 
-	INIT_WORK(&state->commit_work, commit_work);
+	kthread_init_work(&state->commit_kwork, commit_work);
 
 	ret = drm_atomic_helper_prepare_planes(dev, state);
 	if (ret)
@@ -1857,8 +1858,12 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 	 */
 
 	drm_atomic_state_get(state);
+
 	if (nonblock)
-		queue_work(system_unbound_wq, &state->commit_work);
+		worker = drm_atomic_pick_worker(state);
+
+	if (worker)
+		kthread_queue_work(worker, &state->commit_kwork);
 	else
 		commit_tail(state);
 
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index d07c851d255b..8d0ee19953df 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -373,8 +373,18 @@ struct drm_atomic_state {
 	 *
 	 * Work item which can be used by the driver or helpers to execute the
 	 * commit without blocking.
+	 *
+	 * This is deprecated, use commit_kwork.
 	 */
 	struct work_struct commit_work;
+
+	/**
+	 * @commit_kwork:
+	 *
+	 * Work item which can be used by the driver or helpers to execute the
+	 * commit without blocking.
+	 */
+	struct kthread_work commit_kwork;
 };
 
 void __drm_crtc_commit_free(struct kref *kref);
@@ -954,6 +964,27 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
 		      (new_obj_state) = (__state)->private_objs[__i].new_state, 1); \
 	     (__i)++)
 
+/**
+ * drm_atomic_pick_worker - helper to get kworker to use for nonblocking commit
+ * @state: the &drm_atomic_state for the commit
+ *
+ * Pick an appropriate worker for a given atomic update.  The first CRTC
+ * invovled in the atomic update is used to pick the worker, to prevent
+ * serializing multiple pageflips / atomic-updates on indenpendent CRTCs.
+ */
+static inline struct kthread_worker *
+drm_atomic_pick_worker(const struct drm_atomic_state *state)
+{
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+	unsigned i;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i)
+		return crtc->worker;
+
+	return NULL;
+}
+
 /**
  * drm_atomic_crtc_needs_modeset - compute combined modeset need
  * @state: &drm_crtc_state for the CRTC
-- 
2.26.2