Re: [Mesa-dev] [PATCH 4/7] i965/blorp: Optimize manual_blend() for compressed multisampled surfaces.

[Anuj Phogat]

On Thu, Jul 12, 2012 at 10:43 AM, Paul Berry stereotype...@gmail.com wrote:
 When downsampling a compressed multisampled surface, we can take a
 shortcut to downsample any pixels that were completely covered by a
 single primitive.  In this case, the first color value we fetch is the
 correct final color for the downsampled pixel, so we can skip the rest
 of the blending operation.
 ---
  src/mesa/drivers/dri/i965/brw_blorp_blit.cpp |   23 +++
  1 files changed, 23 insertions(+), 0 deletions(-)

 diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp 
 b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
 index 32fd48e..c8db662 100644
 --- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
 +++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
 @@ -1143,6 +1143,26 @@ brw_blorp_blit_program::manual_blend()
}
texel_fetch(texture_data[stack_depth++]);

 +  if (i == 0  key-tex_layout == INTEL_MSAA_LAYOUT_CMS) {
 + /* The Ivy Bridge PRM, Vol4 Part1 p27 (Multisample Control Surface)
 +  * suggests an optimization:
 +  *
 +  * A simple optimization with probable large return in
 +  * performance is to compare the MCS value to zero (indicating
 +  * all samples are on sample slice 0), and sample only from
 +  * sample slice 0 using ld2dss if MCS is zero.
 +  *
 +  * Note that in the case where the MCS value is zero, sampling from
 +  * sample slice 0 using ld2dss and sampling from sample 0 using
 +  * ld2dms are equivalent (since all samples are on sample slice 0).
 +  * Since we have already sampled from sample 0, all we need to do is
 +  * skip the remaining fetches and averaging if MCS is zero.
 +  */
 + brw_CMP(func, vec16(brw_null_reg()), BRW_CONDITIONAL_NZ,
 + mcs_data, brw_imm_ud(0));
 + brw_IF(func, BRW_EXECUTE_16);
 +  }
 +
/* Do count_trailing_one_bits(i) times */
for (int j = count_trailing_one_bits(i); j--  0; ) {
   assert(stack_depth = 2);
 @@ -1169,6 +1189,9 @@ brw_blorp_blit_program::manual_blend()
   brw_imm_f(1.0/num_samples));
}
 }
 +
 +   if (key-tex_layout == INTEL_MSAA_LAYOUT_CMS)
 +  brw_ENDIF(func);
  }

  /**
 --
 1.7.7.6


This is a useful optimization.
Reviewed-by: Anuj Phogat anuj.pho...@gmail.com
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[Mesa-dev] [PATCH 4/7] i965/blorp: Optimize manual_blend() for compressed multisampled surfaces.

[Paul Berry]

When downsampling a compressed multisampled surface, we can take a
shortcut to downsample any pixels that were completely covered by a
single primitive.  In this case, the first color value we fetch is the
correct final color for the downsampled pixel, so we can skip the rest
of the blending operation.
---
 src/mesa/drivers/dri/i965/brw_blorp_blit.cpp |   23 +++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp 
b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
index 32fd48e..c8db662 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
@@ -1143,6 +1143,26 @@ brw_blorp_blit_program::manual_blend()
   }
   texel_fetch(texture_data[stack_depth++]);
 
+  if (i == 0  key-tex_layout == INTEL_MSAA_LAYOUT_CMS) {
+ /* The Ivy Bridge PRM, Vol4 Part1 p27 (Multisample Control Surface)
+  * suggests an optimization:
+  *
+  * A simple optimization with probable large return in
+  * performance is to compare the MCS value to zero (indicating
+  * all samples are on sample slice 0), and sample only from
+  * sample slice 0 using ld2dss if MCS is zero.
+  *
+  * Note that in the case where the MCS value is zero, sampling from
+  * sample slice 0 using ld2dss and sampling from sample 0 using
+  * ld2dms are equivalent (since all samples are on sample slice 0).
+  * Since we have already sampled from sample 0, all we need to do is
+  * skip the remaining fetches and averaging if MCS is zero.
+  */
+ brw_CMP(func, vec16(brw_null_reg()), BRW_CONDITIONAL_NZ,
+ mcs_data, brw_imm_ud(0));
+ brw_IF(func, BRW_EXECUTE_16);
+  }
+
   /* Do count_trailing_one_bits(i) times */
   for (int j = count_trailing_one_bits(i); j--  0; ) {
  assert(stack_depth = 2);
@@ -1169,6 +1189,9 @@ brw_blorp_blit_program::manual_blend()
  brw_imm_f(1.0/num_samples));
   }
}
+
+   if (key-tex_layout == INTEL_MSAA_LAYOUT_CMS)
+  brw_ENDIF(func);
 }
 
 /**
-- 
1.7.7.6

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