Mesa (main): gallium/u_threaded: merge draws faster by merging indexbuf unreferencing

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Module: Mesa
Branch: main
Commit: eb0fa78b686b144882ee0f773b814ca3b7bb7768
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=eb0fa78b686b144882ee0f773b814ca3b7bb7768

Author: Marek Olšák <marek.olsak at amd.com>
Date:   Sun Jun 13 12:13:50 2021 -0400

gallium/u_threaded: merge draws faster by merging indexbuf unreferencing

Instead of N times decrementing the index buffer refcount by 1, decrement
it by N once.

Reviewed-by: Rob Clark <robdclark at chromium.org>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11349>

---

 src/gallium/auxiliary/util/u_inlines.h          | 14 ++++++++++++++
 src/gallium/auxiliary/util/u_threaded_context.c | 10 +++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/gallium/auxiliary/util/u_inlines.h b/src/gallium/auxiliary/util/u_inlines.h
index a8d79a2a79b..958b117ddc3 100644
--- a/src/gallium/auxiliary/util/u_inlines.h
+++ b/src/gallium/auxiliary/util/u_inlines.h
@@ -163,6 +163,20 @@ pipe_resource_reference(struct pipe_resource **dst, struct pipe_resource *src)
    *dst = src;
 }
 
+/**
+ * Subtract the given number of references.
+ */
+static inline void
+pipe_drop_resource_references(struct pipe_resource *dst, int num_refs)
+{
+   int count = p_atomic_add_return(&dst->reference.count, -num_refs);
+
+   assert(count >= 0);
+   /* Underflows shouldn't happen, but let's be safe. */
+   if (count <= 0)
+      pipe_resource_destroy(dst);
+}
+
 /**
  * Same as pipe_surface_release, but used when pipe_context doesn't exist
  * anymore.
diff --git a/src/gallium/auxiliary/util/u_threaded_context.c b/src/gallium/auxiliary/util/u_threaded_context.c
index b77929ad5a3..a8c712a4370 100644
--- a/src/gallium/auxiliary/util/u_threaded_context.c
+++ b/src/gallium/auxiliary/util/u_threaded_context.c
@@ -2969,9 +2969,6 @@ tc_call_draw_single(struct pipe_context *pipe, void *call, uint64_t *last_ptr)
          multi[1].count = next->info.max_index;
          multi[1].index_bias = next->index_bias;
 
-         if (next->info.index_size)
-            tc_drop_resource_reference(next->info.index.resource);
-
          /* Find how many other draws can be merged. */
          next = get_next_call(next, tc_draw_single);
          for (; next != last && is_next_call_a_mergeable_draw(first, next);
@@ -2981,15 +2978,14 @@ tc_call_draw_single(struct pipe_context *pipe, void *call, uint64_t *last_ptr)
             multi[num_draws].count = next->info.max_index;
             multi[num_draws].index_bias = next->index_bias;
             index_bias_varies |= first->index_bias != next->index_bias;
-
-            if (next->info.index_size)
-               tc_drop_resource_reference(next->info.index.resource);
          }
 
          first->info.index_bias_varies = index_bias_varies;
          pipe->draw_vbo(pipe, &first->info, 0, NULL, multi, num_draws);
+
+         /* Since all draws use the same index buffer, drop all references at once. */
          if (first->info.index_size)
-            tc_drop_resource_reference(first->info.index.resource);
+            pipe_drop_resource_references(first->info.index.resource, num_draws);
 
          return call_size(tc_draw_single) * num_draws;
       }