[PATCH] drm/i915/gvt: remove redundant ring id check which cause significant CPU misprediction

[changbin.du at intel.com]

From: Changbin Du <changbin.du at intel.com>

>From perf data, found a significant overhead at ring id check in the
function get_opcode. This inline function is frequently used.

Since Intel static predictor will predict the branch to fall through
so the prediction most fail. This is wasting CPU pipeline resource.
We do not need check the engine id everywhere, it should be reliable.

Signed-off-by: Changbin Du <changbin.du at intel.com>
---
 drivers/gpu/drm/i915/gvt/cmd_parser.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/cmd_parser.c b/drivers/gpu/drm/i915/gvt/cmd_parser.c
index e698c88..41b2c3a 100644
--- a/drivers/gpu/drm/i915/gvt/cmd_parser.c
+++ b/drivers/gpu/drm/i915/gvt/cmd_parser.c
@@ -616,9 +616,6 @@ static inline u32 get_opcode(u32 cmd, int ring_id)
 {
 	struct decode_info *d_info;
 
-	if (ring_id >= I915_NUM_ENGINES)
-		return INVALID_OP;
-
 	d_info = ring_decode_info[ring_id][CMD_TYPE(cmd)];
 	if (d_info == NULL)
 		return INVALID_OP;
@@ -661,9 +658,6 @@ static inline void print_opcode(u32 cmd, int ring_id)
 	struct decode_info *d_info;
 	int i;
 
-	if (ring_id >= I915_NUM_ENGINES)
-		return;
-
 	d_info = ring_decode_info[ring_id][CMD_TYPE(cmd)];
 	if (d_info == NULL)
 		return;
-- 
2.7.4