[dev] [dwm] Avoid requesting MotionNotify events

From: Alexander Monakov <amonakov_AT_ispras.ru>
Date: Sat, 16 Jul 2016 14:33:18 +0300 (MSK)

Hi,

A while ago dwm started requesting MotionNotify events from the X server (that
wasn't always the case). This was added when focus-follows-mouse was implemented
for monitors (in addition to windows) in 2011 by commit b5068e32e9.

This causes lots of useless communication between the X server and dwm every
time the mouse pointer is moved, even when nothing could possibly change as
a result (e.g. if Xinerama is not compiled in, or only one monitor is present).
On my system, the resulting syscalls-per-second count in dwm is about 490, if
the mouse if moved continuously.

The following patch fixes the issue in the minimal way only when Xinerama
support is not enabled at all. I'd find it worthwhile to fix this under
Xinerama too. To outline a partial solution for one-monitor-connected case,
moving XSelectInput to updategeom will allow to request MotionNotify events
only when monitor count is 2 or more. I don't have a patch for this yet, but
I'll be happy to create one if desired.

For multiple-monitors case, it should be possible to avoid MotionNotify events
too, by creating InputOnly subwindows of the root window corresponding to
monitor boundaries, and using EnterNotify events on those to trigger monitor
focus changes. I'm not really familiar with Xlib, so I haven't worked out the
details here, but if there's interest in this solution I can look into it.

Thanks.
Alexander

diff --git a/dwm.c b/dwm.c
index b2bc9bd..304d53b 100644
--- a/dwm.c
+++ b/dwm.c
_AT_@ -1594,8 +1594,11 @@ setup(void)
         XDeleteProperty(dpy, root, netatom[NetClientList]);
         /* select for events */
         wa.cursor = cursor[CurNormal]->cursor;
- wa.event_mask = SubstructureRedirectMask|SubstructureNotifyMask|ButtonPressMask|PointerMotionMask
+ wa.event_mask = SubstructureRedirectMask|SubstructureNotifyMask|ButtonPressMask
                         |EnterWindowMask|LeaveWindowMask|StructureNotifyMask|PropertyChangeMask;
+#ifdef XINERAMA
+ wa.event_mask |= PointerMotionMask;
+#endif
         XChangeWindowAttributes(dpy, root, CWEventMask|CWCursor, &wa);
         XSelectInput(dpy, root, wa.event_mask);
         grabkeys();
Received on Sat Jul 16 2016 - 13:33:18 CEST