[PATCH v4 8/9] gpu/drm/i915: optimize out the case when a range is updated to read only

[jglisse@xxxxxxxxxx]

From: Jérôme Glisse <jglisse@xxxxxxxxxx>

When range of virtual address is updated read only and corresponding
user ptr object are already read only it is pointless to do anything.
Optimize this case out.

Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-rdma@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 9558582c105e..23330ac3d7ea 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -59,6 +59,7 @@ struct i915_mmu_object {
 	struct interval_tree_node it;
 	struct list_head link;
 	struct work_struct work;
+	bool read_only;
 	bool attached;
 };
 
@@ -119,6 +120,7 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 		container_of(_mn, struct i915_mmu_notifier, mn);
 	struct i915_mmu_object *mo;
 	struct interval_tree_node *it;
+	bool update_to_read_only;
 	LIST_HEAD(cancelled);
 	unsigned long end;
 
@@ -128,6 +130,8 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 	/* interval ranges are inclusive, but invalidate range is exclusive */
 	end = range->end - 1;
 
+	update_to_read_only = mmu_notifier_range_update_to_read_only(range);
+
 	spin_lock(&mn->lock);
 	it = interval_tree_iter_first(&mn->objects, range->start, end);
 	while (it) {
@@ -145,6 +149,17 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 		 * object if it is not in the process of being destroyed.
 		 */
 		mo = container_of(it, struct i915_mmu_object, it);
+
+		/*
+		 * If it is already read only and we are updating to
+		 * read only then we do not need to change anything.
+		 * So save time and skip this one.
+		 */
+		if (update_to_read_only && mo->read_only) {
+			it = interval_tree_iter_next(it, range->start, end);
+			continue;
+		}
+
 		if (kref_get_unless_zero(&mo->obj->base.refcount))
 			queue_work(mn->wq, &mo->work);
 
@@ -270,6 +285,7 @@ i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
 	mo->mn = mn;
 	mo->obj = obj;
 	mo->it.start = obj->userptr.ptr;
+	mo->read_only = i915_gem_object_is_readonly(obj);
 	mo->it.last = obj->userptr.ptr + obj->base.size - 1;
 	INIT_WORK(&mo->work, cancel_userptr);
 
-- 
2.17.2