[PATCH 10/13] drm/i915: Wait upon userptr get-user-pages within execbuffer

[Chris Wilson]

This simply hides the EAGAIN caused by userptr when userspace causes
resource contention. However, it is quite beneficial with highly
contended userptr users as we avoid repeating the setup costs and
kernel-user context switches.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Michał Winiarski <michal.winiarski at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c            |  1 +
 drivers/gpu/drm/i915/i915_drv.h            | 10 +++++++++-
 drivers/gpu/drm/i915/i915_gem.c            |  4 +++-
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |  3 +++
 drivers/gpu/drm/i915/i915_gem_userptr.c    | 18 +++++++++++++++---
 5 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 5db5d55fabe5..c1df9be75d4e 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -554,6 +554,7 @@ static void i915_gem_fini(struct drm_i915_private *dev_priv)
 		intel_uc_fini_hw(dev_priv);
 	i915_gem_cleanup_engines(dev_priv);
 	i915_gem_context_fini(dev_priv);
+	i915_gem_cleanup_userptr(dev_priv);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 
 	i915_gem_drain_freed_objects(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4737a09fbe80..4b28cc607fb9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1532,6 +1532,13 @@ struct i915_gem_mm {
 	struct list_head fence_list;
 
 	/**
+	 * Workqueue to fault in userptr pages, flushed by the execbuf
+	 * when required but otherwise left to userspace to try again
+	 * on EAGAIN.
+	 */
+	struct workqueue_struct *userptr_wq;
+
+	/**
 	 * Are we in a non-interruptible section of code like
 	 * modesetting?
 	 */
@@ -3217,7 +3224,8 @@ int i915_gem_set_tiling_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv);
 int i915_gem_get_tiling_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv);
-void i915_gem_init_userptr(struct drm_i915_private *dev_priv);
+int i915_gem_init_userptr(struct drm_i915_private *dev_priv);
+void i915_gem_cleanup_userptr(struct drm_i915_private *dev_priv);
 int i915_gem_userptr_ioctl(struct drm_device *dev, void *data,
 			   struct drm_file *file);
 int i915_gem_get_aperture_ioctl(struct drm_device *dev, void *data,
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3107b1da85af..f9d1f963cdab 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4668,7 +4668,9 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
 	 */
 	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
 
-	i915_gem_init_userptr(dev_priv);
+	ret = i915_gem_init_userptr(dev_priv);
+	if (ret)
+		goto out_unlock;
 
 	ret = i915_gem_init_ggtt(dev_priv);
 	if (ret)
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 7eb59ca5d47e..7bc1b4214b32 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1406,6 +1406,9 @@ static int eb_relocate_slow(struct i915_execbuffer *eb)
 		goto out;
 	}
 
+	/* A frequent cause for EAGAIN are currently unavailable client pages */
+	flush_workqueue(eb->i915->mm.userptr_wq);
+
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret) {
 		mutex_lock(&dev->struct_mutex);
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 58ccf8b8ca1c..66b09163bfba 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -378,7 +378,7 @@ __i915_mm_struct_free(struct kref *kref)
 	mutex_unlock(&mm->i915->mm_lock);
 
 	INIT_WORK(&mm->work, __i915_mm_struct_free__worker);
-	schedule_work(&mm->work);
+	queue_work(mm->i915->mm.userptr_wq, &mm->work);
 }
 
 static void
@@ -598,7 +598,7 @@ __i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj)
 	get_task_struct(work->task);
 
 	INIT_WORK(&work->work, __i915_gem_userptr_get_pages_worker);
-	schedule_work(&work->work);
+	queue_work(to_i915(obj->base.dev)->mm.userptr_wq, &work->work);
 
 	return ERR_PTR(-EAGAIN);
 }
@@ -828,8 +828,20 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 	return 0;
 }
 
-void i915_gem_init_userptr(struct drm_i915_private *dev_priv)
+int i915_gem_init_userptr(struct drm_i915_private *dev_priv)
 {
 	mutex_init(&dev_priv->mm_lock);
 	hash_init(dev_priv->mm_structs);
+
+	dev_priv->mm.userptr_wq =
+		alloc_workqueue("i915-userptr-acquire", WQ_HIGHPRI, 0);
+	if (!dev_priv->mm.userptr_wq)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void i915_gem_cleanup_userptr(struct drm_i915_private *dev_priv)
+{
+	destroy_workqueue(dev_priv->mm.userptr_wq);
 }
-- 
2.11.0