[Mesa-dev] Interesting i965 behavior: more fast color clears not helping dota2

[Eric Anholt]

One of the things I was wondering about for dota2 performance was
whether missing the fast clears was a big performance hit --
particularly with the fips numbers indicating a lot of time spent in
clears.  However, applying this patch:

diff --git a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp b/src/mesa/drivers/dr
index d1933ce..2843ed6 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
@@ -156,7 +156,11 @@ is_color_fast_clear_compatible(struct brw_context *brw,
       if (color->f[i] != 0.0 && color->f[i] != 1.0) {
          perf_debug("Clear color unsupported by fast color clear.  "
                     "Falling back to slow clear.\n");
-         return false;
+         printf("SMASHING FAST CLEAR %f %f %f %f %dx%d\n",
+                color->f[0], color->f[1], color->f[2], color->f[3],
+                brw->ctx.DrawBuffer->_Xmax - brw->ctx.DrawBuffer->_Xmin,
+                brw->ctx.DrawBuffer->_Ymax - brw->ctx.DrawBuffer->_Ymin);
+         return true;
       }
    }
    return true;

produced a lot of output:

SMASHING FAST CLEAR 0.501961 0.501961 0.501961 1.000000 1440x900
SMASHING FAST CLEAR 0.901961 0.901961 0.901961 1.000000 64x64
SMASHING FAST CLEAR 0.501961 0.501961 0.501961 1.000000 1440x900
SMASHING FAST CLEAR 0.901961 0.901961 0.901961 1.000000 64x64

but no performance difference:

anholt at yvain:/home/anholt% ministat before after
x before
+ after
+--------------------------------------------------------------------------+
|   x       x       x   +    +           +   +   *       x                +|
||__________________M___A_|_________________AM__|____________|             |
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   6         13.51         13.64         13.55         13.56   0.056568542
+   6         13.56         13.68         13.61     13.606667   0.042739521
No difference proven at 95.0% confidence

(test was done with the printf run only a single time)
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