State of Zaphod dual screen support

[David Mohr]

On Mon, Mar 1, 2010 at 3:38 PM, Peter Hutterer <peter.hutterer at who-t.net> wrote:
> On Mon, Mar 01, 2010 at 12:41:02AM -0700, David Mohr wrote:
>> On Sun, Feb 28, 2010 at 11:37 PM, Peter Hutterer
>> <peter.hutterer at who-t.net> wrote:
>> > On Sun, Feb 28, 2010 at 11:29:12PM -0700, David Mohr wrote:
>> >> I'm part of the minory who currently uses a Zaphod style dual monitor
>> >> setup with separate X screens for every monitor. When I recently
>> >> upgraded from 7.4 to 7.5, some utilites which I adopted[1] which
>> >> manipulate the mouse cursor started malfunctioning. My two X screens
>> >> are setup to be "apart" so that the mouse does not pass between them,
>> >> and I use my utilities to move the mouse between the two screens. But
>> >> with 7.5 every now and then a condition is triggered where the mouse
>> >> cursor will just continually jump from screen to screen, keeping the X
>> >> server at 100% CPU. I cannot even shut it down using
>> >> CTRL-ALT-Backspace.
>> >>
>> >> I've noticed comments in other threads on this mailing list that
>> >> Zaphod mode is not really supported any more (for completeness' sake,
>> >> I'm using the binary Nvidia drivers). So my question is, is there
>> >> value in trying to track down the bug in Xorg which causes the mouse
>> >> to jump back and forth?
>> >
>> > yes. I've seen this myself and I have not yet identified the issue. it's a
>> > server bug and unrelated to the binary driver. If you can help track this
>> > issue down, it would be much appreciated.
>>
>> Ok. Unfortunately I have not been able to find reliable conditions for
>> triggering the bug. I'll try again and see what I can find.
>
> i found using a wacom tablet with a xinerama setup and then switch back and
> forth triggers it eventually. the problem is the "eventually" bit...

Yes, it's similar for me. One of the tools I use switches the mouse
over when it hits the edge of the screen, so it's warping the pointer
relatively often. I can't reproduce the problem reliably, but if I
keep going back and forth it doesn't take very long to trigger it.

>> Is there any way to get good information out of the running X instance
>> once the bug has been triggered? I can only think of sending a signal
>> to get a core dump, but then I'm not sure how much useful information
>> that would contain.
>
> once it happens, gdb in and single-stepping may be the only approach. a
> backtrace would be great already, just to make sure if you're seeing the
> same problem as I am.

Ugh. Here the trouble begins. When I attach to the process with gdb,
it tells me it's in nvidia_drv.so, which of course doesn't have
debugging symbols. So I can't get a useful backtrace or start to
single step.

Maybe I'll try using the nv or the new noveau driver, but I'd probably
have to adjust my xorg.conf for that. Sigh.

~David