(defvar my-frame (selected-frame))
(defvar my-window (selected-window))
(defvar my-size nil)

(defun w-s-c-f (frame)
  (and (eq frame my-frame)
       (not (equal (cons (window-size my-window) (window-size my-window t))
		   my-size))
       (setq my-size (cons (window-size my-window) (window-size my-window t)))))

(setq window-size-change-functions nil)
(push #'w-s-c-f window-size-change-functions)
(benchmark-run 1000000 (dolist (f window-size-change-functions) (funcall f (selected-frame))))