===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/tmux/server-client.c,v
retrieving revision 1.295
retrieving revision 1.296
diff -u -r1.295 -r1.296
--- src/usr.bin/tmux/server-client.c	2019/09/19 09:02:30	1.295
+++ src/usr.bin/tmux/server-client.c	2019/11/01 20:26:21	1.296
@@ -1,4 +1,4 @@
-/* $OpenBSD: server-client.c,v 1.295 2019/09/19 09:02:30 nicm Exp $ */
+/* $OpenBSD: server-client.c,v 1.296 2019/11/01 20:26:21 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1268,7 +1268,7 @@
 	struct window_pane	*wp;
 	struct winlink		*wl;
 	struct session		*s;
-	int			 focus;
+	int			 focus, attached, resize;
 
 	TAILQ_FOREACH(c, &clients, entry) {
 		server_client_check_exit(c);
@@ -1281,19 +1281,33 @@
 	/*
 	 * Any windows will have been redrawn as part of clients, so clear
 	 * their flags now. Also check pane focus and resize.
+	 *
+	 * As an optimization, panes in windows that are in an attached session
+	 * but not the current window are not resized (this reduces the amount
+	 * of work needed when, for example, resizing an X terminal a
+	 * lot). Windows in no attached session are resized immediately since
+	 * that is likely to have come from a command like split-window and be
+	 * what the user wanted.
 	 */
 	focus = options_get_number(global_options, "focus-events");
 	RB_FOREACH(w, windows, &windows) {
+		attached = resize = 0;
 		TAILQ_FOREACH(wl, &w->winlinks, wentry) {
 			s = wl->session;
-			if (s->attached != 0 && s->curw == wl)
+			if (s->attached != 0)
+				attached = 1;
+			if (s->attached != 0 && s->curw == wl) {
+				resize = 1;
 				break;
+			}
 		}
+		if (!attached)
+			resize = 1;
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->fd != -1) {
 				if (focus)
 					server_client_check_focus(wp);
-				if (wl != NULL)
+				if (resize)
 					server_client_check_resize(wp);
 			}
 			wp->flags &= ~PANE_REDRAW;