[PATCH xf86-video-qxl 2/2] Tune the dfps region tracking to collapse to the bounding rectangle if too many small, incremental, updates are provided.

[Jeremy White <jwhite@xxxxxxxxxxxxxxx>]

Attempting to use x11perf to measure performance revealed a fairly
serious weakness in the dfps code in that use case.  In between
fps ticks, the updated_region would grow to have thousands of
rectangles, which made processing extraordinarily slow.

This patch provides a cap on the number of rectangles inside
a region; once it reaches the cap, we collapse the update_region
to just transmit the bounding rectangle instead.

Signed-off-by: Jeremy White <jwhite@xxxxxxxxxxxxxxx>
---
 src/dfps.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/dfps.c b/src/dfps.c
index a57523b..5db34dc 100644
--- a/src/dfps.c
+++ b/src/dfps.c
@@ -128,12 +128,29 @@ static Bool unaccel (void)
     return FALSE;
 }
 
+
+/* Establish a maximum number of disparate regions we'll track before we just
+   treat the entire bounding rectangle as having changed.
+
+   The number 20 seemed intuitive, and also produced the best results in
+   benchmarking x11perf -circle10 -repeat 1
+*/
+#define DFPS_MAX_UPDATE_REGIONS 20
+static void dfps_update_box(RegionPtr dest, int x_1, int x_2, int y_1, int y_2);
+
 static void dfps_update_region(RegionPtr dest, RegionPtr src)
 {
     Bool throwaway_bool;
 
     RegionAppend(dest, src);
     RegionValidate(dest, &throwaway_bool);
+    if (RegionNumRects(dest) > DFPS_MAX_UPDATE_REGIONS)
+    {
+        struct pixman_box16 box = * (RegionExtents(dest));
+        RegionUninit(dest);
+        RegionInit(dest, NULL, 0);
+        dfps_update_box(dest, box.x1, box.x2, box.y1, box.y2);
+    }
 }
 
 static void dfps_update_box(RegionPtr dest, int x_1, int x_2, int y_1, int y_2)
-- 
1.7.10.4

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