Mouse lag and ksmserver

[Patrick O'Callaghan]

It's hard to know whether these two things are connected, but I'll
mention them together since they seem to have been correlated at least
once:

I often find that after being logged into Plasma session for a few
days, the cursor starts to lag noticeably behind my wireless
(Bluetooth) mouse movement, to the extent that the mouse becomes quite
difficult to use. It's hard to determine just what causes this. At one
point I suspected either Chrome or Firefox, perhaps because some Web
page was very loaded with Javascript, but last time I killed both of
them and it seemed to make no difference.

I have a second mouse (MS wireless connected via a USB dongle) and its
behaviour is always entirely normal, i.e. no lag. I've tried using
Gnome but haven't managed to reproduce this behaviour, though I also
haven't tried very hard.

When this problem cropped up just now, after several days of not
appearing, I checked "top" and found ksmserver taking 13% of CPU, far
above anything else. This is an 8-core Intel i7 with 16GB of RAM (and
root on an SSD).

I logged out of the session and logged into a console. ksmserver CPU
usage went up to 100% and stayed there. I rebooted and everything went
back to normal, i.e. no mouse lag and ksmserver taking no appreciable
CPU time.

Any ideas would be welcome.

poc