Slow GTK3 redisplay

[Dmitry Antipov]

Some time ago I did the following simple redisplay benchmark:

(defun scroll-benchmark ()
  (interactive)
  (let ((oldgc gcs-done)
        (oldtime (float-time)))
    (condition-case nil (while t (scroll-up) (redisplay))
      (error (message "GCs: %d Elapsed time: %f seconds"
                      (- gcs-done oldgc) (- (float-time) oldtime))))))

And here are some results of running the code above over xdisp.c,
with different X toolkits and without it. Of course, emacs -Q was used.
GTK3 is 3.2.4, GTK2 is 2.24.8, OpenMotif is 2.3.3, Xaw3d 1.5E, Xaw 1.0.8.

Default GUI means menu bar, tool bar and scroll bar enabled. Minimal GUI
means all of the above is disabled, i.e. the frame state after

(progn (menu-bar-mode 0) (tool-bar-mode 0) (scroll-bar-mode -1)).

Numbers are in seconds.

          Default GUI Minimal GUI
GTK3:        108          34
GTK2:         41          34
OpenMotif:    36          34
Lucid:        38          34
None:         36          33

Here GTK3 GUI is _painfully_ slow. Can someone explain this? Is something
wrong with my GTK3 setup? Am I running heavyweight theme, or what?

Dmitry