[Mesa-dev] [PATCH] util/slab: add slab_free_fast()

[Rob Clark]

From: Rob Clark <robdclark at chromium.org>

I noticed slab_free() showing up at the top of perf results in
gl_driver2, due to "streaming" GPU state objects, which are allocated
and destroyed within a single draw call.

In this case, it is guaranteed that we free on the same child pool,
from the same (only) thread accessing the child pool.  So add a faster,
but more restricted version of slab_free() to cut the overhead.

Signed-off-by: Rob Clark <robdclark at chromium.org>
---
 src/util/slab.c | 20 ++++++++++++++++++++
 src/util/slab.h |  1 +
 2 files changed, 21 insertions(+)

diff --git a/src/util/slab.c b/src/util/slab.c
index 62634034fdc..21076a80238 100644
--- a/src/util/slab.c
+++ b/src/util/slab.c
@@ -276,6 +276,26 @@ void slab_free(struct slab_child_pool *pool, void *ptr)
    }
 }
 
+/**
+ * Similar to slab_free(), except that freeing an object in a different pool
+ * from the one it was allocated from is *not* allowed.
+ */
+void slab_free_fast(struct slab_child_pool *pool, void *ptr)
+{
+   struct slab_element_header *elt = ((struct slab_element_header*)ptr - 1);
+
+   CHECK_MAGIC(elt, SLAB_MAGIC_ALLOCATED);
+   SET_MAGIC(elt, SLAB_MAGIC_FREE);
+
+   assert(p_atomic_read(&elt->owner) == (intptr_t)pool);
+
+   /* This is the simple case: The caller guarantees that we can safely
+    * access the free list.
+    */
+   elt->next = pool->free;
+   pool->free = elt;
+}
+
 /**
  * Allocate an object from the slab. Single-threaded (no mutex).
  */
diff --git a/src/util/slab.h b/src/util/slab.h
index 5a25adaf7f4..9748cd95858 100644
--- a/src/util/slab.h
+++ b/src/util/slab.h
@@ -78,6 +78,7 @@ void slab_create_child(struct slab_child_pool *pool,
 void slab_destroy_child(struct slab_child_pool *pool);
 void *slab_alloc(struct slab_child_pool *pool);
 void slab_free(struct slab_child_pool *pool, void *ptr);
+void slab_free_fast(struct slab_child_pool *pool, void *ptr);
 
 struct slab_mempool {
    struct slab_parent_pool parent;
-- 
2.21.0