drm/i915: Lazily unbind vma on close

When userspace is passing around swapbuffers using DRI, we frequently
have to open and close the same object in the foreign address space.
This shows itself as the same object being rebound at roughly 30fps
(with a second object also being rebound at 30fps), which involves us
having to rewrite the page tables and maintain the drm_mm range manager
every time.

However, since the object still exists and it is only the local handle
that disappears, if we are lazy and do not unbind the VMA immediately
when the local user closes the object but defer it until the GPU is
idle, then we can reuse the same VMA binding. We still have to be
careful to mark the handle and lookup tables as closed to maintain the
uABI, just allowing the underlying VMA to be resurrected if the user is
able to access the same object from the same context again.

If the object itself is destroyed (neither userspace keeping a handle to
it), the VMA will be reaped immediately as usual.

In the future, this will be even more useful as instantiating a new VMA
for use on the GPU will become heavier. A nuisance indeed, so nip it in
the bud.

v2: s/__i915_vma_final_close/i915_vma_destroy/ etc.
v3: Leave a hint as to why we deferred the unbind on close.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180503195115.22309-1-chris@chris-wilson.co.uk

1 files changed, 56 insertions, 17 deletions

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 4bda3bd29bf5..9324d476e0a7 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -46,8 +46,6 @@ i915_vma_retire(struct i915_gem_active *active, struct i915_request *rq)
 
 	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
 	list_move_tail(&vma->vm_link, &vma->vm->inactive_list);
-	if (unlikely(i915_vma_is_closed(vma) && !i915_vma_is_pinned(vma)))
-		WARN_ON(i915_vma_unbind(vma));
 
 	GEM_BUG_ON(!i915_gem_object_is_active(obj));
 	if (--obj->active_count)
@@ -232,7 +230,6 @@ i915_vma_instance(struct drm_i915_gem_object *obj,
 	if (!vma)
 		vma = vma_create(obj, vm, view);
 
-	GEM_BUG_ON(!IS_ERR(vma) && i915_vma_is_closed(vma));
 	GEM_BUG_ON(!IS_ERR(vma) && i915_vma_compare(vma, vm, view));
 	GEM_BUG_ON(!IS_ERR(vma) && vma_lookup(obj, vm, view) != vma);
 	return vma;
@@ -684,13 +681,43 @@ err_unpin:
 	return ret;
 }
 
-static void i915_vma_destroy(struct i915_vma *vma)
+void i915_vma_close(struct i915_vma *vma)
+{
+	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
+
+	GEM_BUG_ON(i915_vma_is_closed(vma));
+	vma->flags |= I915_VMA_CLOSED;
+
+	/*
+	 * We defer actually closing, unbinding and destroying the VMA until
+	 * the next idle point, or if the object is freed in the meantime. By
+	 * postponing the unbind, we allow for it to be resurrected by the
+	 * client, avoiding the work required to rebind the VMA. This is
+	 * advantageous for DRI, where the client/server pass objects
+	 * between themselves, temporarily opening a local VMA to the
+	 * object, and then closing it again. The same object is then reused
+	 * on the next frame (or two, depending on the depth of the swap queue)
+	 * causing us to rebind the VMA once more. This ends up being a lot
+	 * of wasted work for the steady state.
+	 */
+	list_add_tail(&vma->closed_link, &vma->vm->i915->gt.closed_vma);
+}
+
+void i915_vma_reopen(struct i915_vma *vma)
+{
+	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
+
+	if (vma->flags & I915_VMA_CLOSED) {
+		vma->flags &= ~I915_VMA_CLOSED;
+		list_del(&vma->closed_link);
+	}
+}
+
+static void __i915_vma_destroy(struct i915_vma *vma)
 {
 	int i;
 
 	GEM_BUG_ON(vma->node.allocated);
-	GEM_BUG_ON(i915_vma_is_active(vma));
-	GEM_BUG_ON(!i915_vma_is_closed(vma));
 	GEM_BUG_ON(vma->fence);
 
 	for (i = 0; i < ARRAY_SIZE(vma->last_read); i++)
@@ -699,6 +726,7 @@ static void i915_vma_destroy(struct i915_vma *vma)
 
 	list_del(&vma->obj_link);
 	list_del(&vma->vm_link);
+	rb_erase(&vma->obj_node, &vma->obj->vma_tree);
 
 	if (!i915_vma_is_ggtt(vma))
 		i915_ppgtt_put(i915_vm_to_ppgtt(vma->vm));
@@ -706,15 +734,30 @@ static void i915_vma_destroy(struct i915_vma *vma)
 	kmem_cache_free(to_i915(vma->obj->base.dev)->vmas, vma);
 }
 
-void i915_vma_close(struct i915_vma *vma)
+void i915_vma_destroy(struct i915_vma *vma)
 {
-	GEM_BUG_ON(i915_vma_is_closed(vma));
-	vma->flags |= I915_VMA_CLOSED;
+	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
 
-	rb_erase(&vma->obj_node, &vma->obj->vma_tree);
+	GEM_BUG_ON(i915_vma_is_active(vma));
+	GEM_BUG_ON(i915_vma_is_pinned(vma));
+
+	if (i915_vma_is_closed(vma))
+		list_del(&vma->closed_link);
+
+	WARN_ON(i915_vma_unbind(vma));
+	__i915_vma_destroy(vma);
+}
+
+void i915_vma_parked(struct drm_i915_private *i915)
+{
+	struct i915_vma *vma, *next;
 
-	if (!i915_vma_is_active(vma) && !i915_vma_is_pinned(vma))
-		WARN_ON(i915_vma_unbind(vma));
+	list_for_each_entry_safe(vma, next, &i915->gt.closed_vma, closed_link) {
+		GEM_BUG_ON(!i915_vma_is_closed(vma));
+		i915_vma_destroy(vma);
+	}
+
+	GEM_BUG_ON(!list_empty(&i915->gt.closed_vma));
 }
 
 static void __i915_vma_iounmap(struct i915_vma *vma)
@@ -804,7 +847,7 @@ int i915_vma_unbind(struct i915_vma *vma)
 		return -EBUSY;
 
 	if (!drm_mm_node_allocated(&vma->node))
-		goto destroy;
+		return 0;
 
 	GEM_BUG_ON(obj->bind_count == 0);
 	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
@@ -841,10 +884,6 @@ int i915_vma_unbind(struct i915_vma *vma)
 
 	i915_vma_remove(vma);
 
-destroy:
-	if (unlikely(i915_vma_is_closed(vma)))
-		i915_vma_destroy(vma);
-
 	return 0;
 }