Randomly garbled display, secondary screen, dual-head

[Filofel]

Dual-head display (Matrox G450, Xinerama, 1280x1024 on each screen).
The problem appeared immediately after migrating from drapper 6.06 to edgy 6.10
When moving a window fast enough on the secondary screen, the "trailing" effect behind the window is not erased from the desktop and leaves random patterns behind (on the desktop background). When moving the window very slowly, the problem does not happen.
Displaying then closing any window, or moving a window very slowly on the garbled desktop properly repaints the desktop background.
When moving a window over another window, the underneath window always repaints properly (i.e. doesn't endup garbled).
This never happens on the primary screen.
A much less frequent form of the problem is that once in a while, a graphical object is painted garbled in an application window (for instance, the Google logo in Firefox). In this case, the garbled spot is exactly the rectangle that should have contained the graphical object.

[Filofel (filofel)]

Problem has simply disappeared today, I can't reproduce it - even after trying hard.
I have no idea why it went away (nor what created in the first place, apart from the upgrade to edgy, since it appeared at this time).
Before I reported it, I had made sure it wasn't a one-shot glitch I could fix: I checked a bunch of various issues including xorg.log (there was no error nor anything unusual there), rebooted the machine a couple of times just to make sure this wasn't a temp upgrade glitch, etc.

I'm just puzzled.
As far as I'm concerned, Bug #68968 can be considered closed.

I apologize for the trouble :-( /Ph.

[Filofel (filofel)]

Scoop:
The problem came back as initially described (sigh).

The current status is that on some boots, the problem randomly shows up (and sticks), and on some others, it doesn't.
This is happening on a vanilla 6.06 upgraded to 6.10, with very little customization or added software at this point.

[Filofel (filofel)]

Confirmed:
The problem might or might not show up on a given session after a reboot.

Whenever it reproduces, I will see how it resists / recurs when login off / login back and Ctrl-Alt-Bksp ing.

[Bryce Harrington (bryce)]

It may be helpful to attach your /etc/X11/xorg.conf and /var/log/Xorg.0.log, to assist in troubleshooting. Also the output of lshw and/or lspci if you have it could be helpful.

Given that you see it happening on one monitor but not the other, I wonder if it could be differences or incompatibilities between the two monitors or their hardware, so knowing more details about your hardware configuration could be handy. Could also be the driver possibly.

[Filofel (filofel)]

> It may be helpful to attach your /etc/X11/xorg.conf
> and /var/log/Xorg.0.log, to assist in troubleshooting.
> Also the output of lshw and/or lspci if you have it could
> be helpful.

Thanks for your suggestions.
Will do next time the problem re-appears.
I will also compare the log on a boot that results in the problem with the log on a boot that doesn't reproduce it, just in case.
I saw the problem again a few days ago: That time, in addition to what's described above, the bottom 1/5 of the secondary screen was constantly flickering erroneous pixels. Everything came back to normal after restarting X thru a Ctrl-Alt-Bksp sequence.

> I wonder if it could be differences or incompatibilities
> between the two monitors

I don't think so, the two monitors are exactly identical, same brand (Hyundai), same model, bought at the same time, same Xorg parms. I would rather suspect the fact that the Matrox G400 hardware and/or driver doesn't handle the primary and secondary screen exactly the same way.

[Filofel (filofel)]

Bryce,

There we are.
The attached files contains the xorg.conf, a log after a "good" xorg session, and a log after a "bad" one.

Thanks for your assistance!

[Bryce Harrington (bryce)]

[This is an automatic notification.]

Hi REPORTER,

This bug was reported against an earlier version of Ubuntu, can you
test if it still occurs on Lucid?

Please note we also provide technical support for older versions of
Ubuntu, but not in the bug tracker. Instead, to raise the issue through
normal support channels, please see:

    http://www.ubuntu.com/support

If you are the original reporter and can still reproduce the issue on
Lucid, please run the following command to refresh the report:

  apport-collect BUGNUMBER

If you are not the original reporter, please file a new bug report, so
we can work with you as the original reporter instead (you can reference
bug BUGNUMBER in your report if you think it may be related):

  ubuntu-bug xorg

If by chance you can no longer reproduce the issue on Lucid or if you
feel it is no longer relevant, please mark the bug report 'Fix Released'
or 'Invalid' as appropriate, at the following URL:

  https://bugs.launchpad.net/ubuntu/+bug/BUGNUMBER

[Bryce Harrington (bryce)]

[This is an automatic notification.]

Hi Filofel,

This bug was reported against an earlier version of Ubuntu, can you
test if it still occurs on Lucid?

Please note we also provide technical support for older versions of
Ubuntu, but not in the bug tracker. Instead, to raise the issue through
normal support channels, please see:

    http://www.ubuntu.com/support

If you are the original reporter and can still reproduce the issue on
Lucid, please run the following command to refresh the report:

  apport-collect 68968

If you are not the original reporter, please file a new bug report, so
we can work with you as the original reporter instead (you can reference
bug 68968 in your report if you think it may be related):

  ubuntu-bug xorg

If by chance you can no longer reproduce the issue on Lucid or if you
feel it is no longer relevant, please mark the bug report 'Fix Released'
or 'Invalid' as appropriate, at the following URL:

  https://bugs.launchpad.net/ubuntu/+bug/68968