drm/i915: Replace execbuf vma ht with an idr

This was the competing idea long ago, but it was only with the rewrite
of the idr as an radixtree and using the radixtree directly ourselves,
along with the realisation that we can store the vma directly in the
radixtree and only need a list for the reverse mapping, that made the
patch performant enough to displace using a hashtable. Though the vma ht
is fast and doesn't require any extra allocation (as we can embed the node
inside the vma), it does require a thread for resizing and serialization
and will have the occasional slow lookup. That is hairy enough to
investigate alternatives and favour them if equivalent in peak performance.
One advantage of allocating an indirection entry is that we can support a
single shared bo between many clients, something that was done on a
first-come first-serve basis for shared GGTT vma previously. To offset
the extra allocations, we create yet another kmem_cache for them.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170816085210.4199-5-chris@chris-wilson.co.uk

1 files changed, 22 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_object.h b/drivers/gpu/drm/i915/i915_gem_object.h
index 3baa341432db..c30d8f808185 100644
--- a/drivers/gpu/drm/i915/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/i915_gem_object.h
@@ -38,6 +38,19 @@
 
 struct drm_i915_gem_object;
 
+/*
+ * struct i915_lut_handle tracks the fast lookups from handle to vma used
+ * for execbuf. Although we use a radixtree for that mapping, in order to
+ * remove them as the object or context is closed, we need a secondary list
+ * and a translation entry (i915_lut_handle).
+ */
+struct i915_lut_handle {
+	struct list_head obj_link;
+	struct list_head ctx_link;
+	struct i915_gem_context *ctx;
+	u32 handle;
+};
+
 struct drm_i915_gem_object_ops {
 	unsigned int flags;
 #define I915_GEM_OBJECT_HAS_STRUCT_PAGE BIT(0)
@@ -89,7 +102,15 @@ struct drm_i915_gem_object {
 	 * They are also added to @vma_list for easy iteration.
 	 */
 	struct rb_root vma_tree;
-	struct i915_vma *vma_hashed;
+
+	/**
+	 * @lut_list: List of vma lookup entries in use for this object.
+	 *
+	 * If this object is closed, we need to remove all of its VMA from
+	 * the fast lookup index in associated contexts; @lut_list provides
+	 * this translation from object to context->handles_vma.
+	 */
+	struct list_head lut_list;
 
 	/** Stolen memory for this object, instead of being backed by shmem. */
 	struct drm_mm_node *stolen;