[Mesa-dev] [PATCH V2] i965 : Optimize atom state flag checks

[aravindan.muthukumar at intel.com]

From: Aravindan Muthukumar <aravindan.muthukumar at intel.com>

This patch improves CPI Rate(Cycles per Instruction)
and branch mispredict for i965. The function check_state()
was showing CPI retired rate.

Performance stats with android:
CPI retired lowered by 28% (lower is better)
Branch missprediction lowered by 13% (lower is better)
3DMark improved by 2%

The dissassembly doesn't show difference, although above
results were observed with patch.

Signed-off-by: Aravindan Muthukumar <aravindan.muthukumar at intel.com>
Signedd-off-by: Yogesh Marathe <yogesh.marathe at intel.com>
Tested-by: Asish <asish at intel.com>
---

Changes since V1:
- Removed memset() change
- Changed commit message as per review comments

 src/mesa/drivers/dri/i965/brw_defines.h      |  4 ++++
 src/mesa/drivers/dri/i965/brw_state_upload.c | 12 ++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index 2a8dbf8..8c9a510 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -1687,3 +1687,7 @@ enum brw_pixel_shader_coverage_mask_mode {
 # define CSDBG2_CONSTANT_BUFFER_ADDRESS_OFFSET_DISABLE (1 << 4)
 
 #endif
+
+/* Checking the state of mesa and brw before emitting atoms */
+#define CHECK_BRW_STATE(a,b) ((a.mesa & b.mesa) | (a.brw & b.brw))
+
diff --git a/src/mesa/drivers/dri/i965/brw_state_upload.c b/src/mesa/drivers/dri/i965/brw_state_upload.c
index acaa97e..1c8b969 100644
--- a/src/mesa/drivers/dri/i965/brw_state_upload.c
+++ b/src/mesa/drivers/dri/i965/brw_state_upload.c
@@ -443,10 +443,8 @@ check_and_emit_atom(struct brw_context *brw,
                     struct brw_state_flags *state,
                     const struct brw_tracked_state *atom)
 {
-   if (check_state(state, &atom->dirty)) {
       atom->emit(brw);
       merge_ctx_state(brw, state);
-   }
 }
 
 static inline void
@@ -541,7 +539,10 @@ brw_upload_pipeline_state(struct brw_context *brw,
 	 const struct brw_tracked_state *atom = &atoms[i];
 	 struct brw_state_flags generated;
 
-         check_and_emit_atom(brw, &state, atom);
+         /* Checking the state and emitting atoms */
+         if (CHECK_BRW_STATE(state, atom->dirty)) {
+            check_and_emit_atom(brw, &state, atom);
+         }
 
 	 accumulate_state(&examined, &atom->dirty);
 
@@ -558,7 +559,10 @@ brw_upload_pipeline_state(struct brw_context *brw,
       for (i = 0; i < num_atoms; i++) {
 	 const struct brw_tracked_state *atom = &atoms[i];
 
-         check_and_emit_atom(brw, &state, atom);
+         /* Checking the state and emitting atoms */
+         if (CHECK_BRW_STATE(state, atom->dirty)) {
+            check_and_emit_atom(brw, &state, atom);
+         }
       }
    }
 
-- 
2.7.4