[Qemu-devel] udev 42-qemu-usb.rules considered harmful?

[Michael Tokarev]

Hello.

I noticed that "some" versions of linux guests shows quite
bad behavour of mouse cursor: it freezes after some idle
time, and when you move mouse, it jumps after some delay
to rather distant position.  So, mouse becomes "freezy/jumpy",
so to say.

Quite some painful debugging pointed to the following
udev rule:

---- /lib/udev/rules.d/42-qemu-usb.rules ----
#
# Enable autosuspend for qemu emulated usb hid devices.
#
# Note that there are buggy qemu versions which advertise remote
# wakeup support but don't actually implement it correctly.  This
# is the reason why we need a match for the serial number here.
# The serial number "42" is used to tag the implementations where
# remote wakeup is working.
#
ACTION=="add", SUBSYSTEM=="usb", ATTR{product}=="QEMU USB Tablet", 
ATTR{serial}=="42", TEST=="power/control", ATTR{power/control}="auto"
---- end ----

(And a few other similar rules, for other QEMU USB devices).

Removing this rule restores correct mouse behavour.

As far as I can see, this rule is to reduce polling interrupt
frequency, but apparently it does not help: any usb device
connected to guest, and the host CPU usage rises anyway, with
or without this rule.

Now the question: should we remove this rule?  Why it is needed
to start with?

(qemu version 1.1, but the same bad behavour happens with other
versions too).

Thanks,

/mjt