[perf] Calibrate tests to run for at least 2 seconds

By ensuring that tests take longer than a couple of seconds we eliminate
systematic errors in our measurements. However, we also effectively
eliminate the synchronisation overhead. To compensate, we attempt to
estimate the overhead by reporting the difference between a single
instance and the minimum averaged instance.

1 files changed, 5 insertions, 2 deletions

diff --git a/perf/subimage_copy.c b/perf/subimage_copy.c
index 25b16cc2c..9bec2fb01 100644
--- a/perf/subimage_copy.c
+++ b/perf/subimage_copy.c
@@ -35,17 +35,20 @@
  */
 
 static cairo_perf_ticks_t
-do_subimage_copy (cairo_t *cr, int width, int height)
+do_subimage_copy (cairo_t *cr, int width, int height, int loops)
 {
     cairo_rectangle (cr, 2, 2, 4, 4);
     cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
 
     cairo_perf_timer_start ();
 
-    cairo_fill (cr);
+    while (loops--)
+	cairo_fill_preserve (cr);
 
     cairo_perf_timer_stop ();
 
+    cairo_new_path (cr);
+
     return cairo_perf_timer_elapsed ();
 }