Re: Roundtrip in gdk_flush()

[Soeren Sandmann <sandmann daimi au dk>]

Owen Taylor <otaylor redhat com> writes:

> I think except on SMP machines, the 25% in gdk_flush() doesn't
> indicate any real problems... we are just waiting for the X server to
> catch up.  (Even in SMP cases, I don't think there is any point in
> getting ahead of the X server; we'd just end up blocking with full
> request queues a little later anyways.)

Well, I did some tests:

I instrumented gtk with this patch to gtkcontainer.c:

alpine:~/vertigo/gtk+/gtk% cvs diff -u gtkcontainer.c
Index: gtkcontainer.c
===================================================================
RCS file: /cvs/gnome/gtk+/gtk/gtkcontainer.c,v
retrieving revision 1.107
diff -u -r1.107 gtkcontainer.c
--- gtkcontainer.c	20 Mar 2002 21:47:00 -0000	1.107
+++ gtkcontainer.c	25 Mar 2002 19:24:40 -0000
@@ -976,6 +976,10 @@
   return GTK_IS_RESIZE_CONTAINER (widget) ? (GtkContainer*) widget : NULL;
 }
 
+static GTimer *timer = NULL;
+static gdouble total = 0.0;
+static guint n_resizes = 0;
+	     
 static gboolean
 gtk_container_idle_sizer (gpointer data)
 {
@@ -1003,6 +1007,9 @@
 
   gdk_window_process_all_updates ();
 
+  total += g_timer_elapsed (timer, NULL);
+  g_print ("time to resize: %f\n", total / ++n_resizes);
+
   GDK_THREADS_LEAVE ();
 
   return FALSE;
@@ -1041,9 +1048,16 @@
 		{
 		  GTK_PRIVATE_SET_FLAG (resize_container, GTK_RESIZE_PENDING);
 		  if (container_resize_queue == NULL)
-		    gtk_idle_add_priority (GTK_PRIORITY_RESIZE,
+		    {
+		      if (!timer)
+			timer = g_timer_new ();
+		      
+		      g_timer_reset (timer);
+		      
+		      gtk_idle_add_priority (GTK_PRIORITY_RESIZE,
 					   gtk_container_idle_sizer,
 					   NULL);
+		    }
 		  container_resize_queue = g_slist_prepend (container_resize_queue, resize_container);
 		}
 	      break;

and then I tried opaque resizing the notebook test in testgtk.c with
various implementations of gdk_flush():


(a) Unmodified gtk+ with gdk_flush() == XSync ():             0.019730
(b) gtk with gdk_flush() == XFlush():                         0.005460
(c) with gdk_window_process_all_updates() calling XFlush()    0.005903
(d) calling gdk_flush() == XSync in idle handler              0.005445


So it seems that getting rid of the round trip does have a significant
impact on the time to respond to events. 


Søren