Created attachment 115835 [details]
my xorg.conf

My xorg setup is based on two independent screen (see attached xorg.conf). Most
of the time the Xorg process eat 100% of one CPU core.

I will try to explain what I think is the problem and the fix (or workaround) I
made to the nouveau code.

Basically, the problem is that nouveau add a socket to the xorg socket list but
does not register a handler that will be able to deal with it. When data is
received on this socket the Select call in xorg-server/os/WaitFor.c will return
but the data will not be read. When Select is called again it returns
immediately because data was not read, and again, and again, resulting in 100%
CPU core consumption.

Now, some details (based on xf86-video-nouveau-1.0.11 source code)
To add a socket in the xorg server list AddGeneralSocket is used.
In src/drmmode_display.c AddGeneralSocket is called in two places: line 1605
(via drmmode_uevent_init and line 1554) and 1610. If line 1608 condition is not
meet, a socket is added without an handler so drmmode_wakeup_handler will never
be called with correct data.

My solution is to add a new handler that will only handle the udev part when
line 1608 condition is not meet. See attached patch.