Commit 43c29e1f authored Apr 06, 2017 by Changbin Du Committed by Zhenyu Wang Apr 12, 2017

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

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@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

parent 80901ca8

drivers/gpu/drm/i915/gvt/cmd_parser.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -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;