Mesa (master): panfrost: Compact the bo_access readers array

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Module: Mesa
Branch: master
Commit: 5e8386c606293de4f9cbbc2666a9e9e3758b6b29
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5e8386c606293de4f9cbbc2666a9e9e3758b6b29

Author: Icecream95 <ixn at keemail.me>
Date:   Thu Jan 16 09:51:17 2020 +1300

panfrost: Compact the bo_access readers array

Previously, the array bo_access->readers was only cleared when there
were no unsignaled fences, which in some situations never happened.

That resulted in the array having thousands of NULL pointers, but only
a handful of active readers.

With this patch, all the unsignaled readers are moved to the front of
the array, effectively building a new array only containing the active
readers in-place. This results in the readers array usually only having
a couple of elements.

Reviewed-by: Boris Brezillon <boris.brezillon at collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3419>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3419>

---

 src/gallium/drivers/panfrost/pan_job.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/gallium/drivers/panfrost/pan_job.c b/src/gallium/drivers/panfrost/pan_job.c
index 1b7d370b998..8ec00022999 100644
--- a/src/gallium/drivers/panfrost/pan_job.c
+++ b/src/gallium/drivers/panfrost/pan_job.c
@@ -346,7 +346,9 @@ panfrost_bo_access_gc_fences(struct panfrost_context *ctx,
                 access->writer = NULL;
         }
 
-        unsigned nreaders = 0;
+        struct panfrost_batch_fence **readers_array = util_dynarray_begin(&access->readers);
+        struct panfrost_batch_fence **new_readers = readers_array;
+
         util_dynarray_foreach(&access->readers, struct panfrost_batch_fence *,
                               reader) {
                 if (!(*reader))
@@ -356,12 +358,15 @@ panfrost_bo_access_gc_fences(struct panfrost_context *ctx,
                         panfrost_batch_fence_unreference(*reader);
                         *reader = NULL;
                 } else {
-                        nreaders++;
+                        /* Build a new array of only unsignaled fences in-place */
+                        *(new_readers++) = *reader;
                 }
         }
 
-        if (!nreaders)
-                util_dynarray_clear(&access->readers);
+        if (!util_dynarray_resize(&access->readers, struct panfrost_batch_fence *,
+                                  new_readers - readers_array) &&
+            new_readers != readers_array)
+                unreachable("Invalid dynarray access->readers");
 }
 
 /* Collect signaled fences to keep the kernel-side syncobj-map small. The