[Mesa-dev] [PATCH 2/2] intel: Reserve enough space to finish occlusion queries on Gen6.

[Kenneth Graunke]

After realizing that brw_finish_batch emitted some final PIPE_CONTROLs
to record occlusion queries, Chris noted that we probably hadn't
reserved enough space to actually emit them.

Reserving a full 60 bytes seems a bit harsh, since we only need that
much if occlusion queries are actually active.  Plus, 28 bytes would be
sufficient for Gen7, and 24 for Gen4-5.

We could optimize this in the future, but it doesn't seem too critical.

NOTE: This is a candidate for stable release branches.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Eric Anholt <eric at anholt.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53311
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_vtbl.c           |    4 ++++
 src/mesa/drivers/dri/intel/intel_batchbuffer.h |   12 +++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

We used to reserve 16 bytes.  8 are clearly for the MI_BATCHBUFFER_END
and the MI_NOOP.  Chris thought the other 8 were just extra breathing
room, which seems accurate.  This patch eliminates those extra bytes,
so if they actually -are- used for something, we could be in trouble.

diff --git a/src/mesa/drivers/dri/i965/brw_vtbl.c b/src/mesa/drivers/dri/i965/brw_vtbl.c
index e76b264..9951e7d 100644
--- a/src/mesa/drivers/dri/i965/brw_vtbl.c
+++ b/src/mesa/drivers/dri/i965/brw_vtbl.c
@@ -147,6 +147,10 @@ brw_update_draw_buffer(struct intel_context *intel)
 /**
  * called from intel_batchbuffer_flush and children before sending a
  * batchbuffer off.
+ *
+ * Note that ALL state emitted here must fit in the reserved space
+ * at the end of a batchbuffer.  If you add more GPU state, increase
+ * the BATCH_RESERVED macro.
  */
 static void brw_finish_batch(struct intel_context *intel)
 {
diff --git a/src/mesa/drivers/dri/intel/intel_batchbuffer.h b/src/mesa/drivers/dri/intel/intel_batchbuffer.h
index d2744e4..b8b60cd 100644
--- a/src/mesa/drivers/dri/intel/intel_batchbuffer.h
+++ b/src/mesa/drivers/dri/intel/intel_batchbuffer.h
@@ -11,7 +11,17 @@
 extern "C" {
 #endif
 
-#define BATCH_RESERVED 16
+/**
+ * Number of bytes to reserve for commands necessary to complete a batch.
+ *
+ * This includes:
+ * - MI_BATCHBUFFER_END (4 bytes)
+ * - Optional MI_NOOP for ensuring the batch length is qword aligned (4 bytes)
+ * - Any state emitted by vtbl->finish_batch()
+ *   - On 965+, this means ending occlusion queries (on Gen6, which has the
+ *     most workaround flushes, this can be as much as (4+4+5)*4 = 52 bytes)
+ */
+#define BATCH_RESERVED 60
 
 struct intel_batchbuffer;
 
-- 
1.7.10.4