Bug#500281: xserver-xorg-video-savage: freezes the entire system with some OpenGL screensavers

[Brice Goglin <Brice.Goglin@ens-lyon.org>]

Francesco Poli wrote:
> On Fri, 25 Sep 2009 22:28:06 +0200 Brice Goglin wrote:
>
>   
>> Francesco Poli wrote:
>>     
>>> Nonetheless, the test was not completely error free.  Indeed, some
>>> worrying entries were logged to /var/log/kern.log:
>>>
>>>
>>> [  582.975686] Xorg:5396 conflicting memory types 90000000-95000000 uncached-minus<->write-combining
>>>       
> [...]
>   
>>> As a consequence, I am *not* sure that the bug can be safely considered
>>> as fixed...
>>>   
>>>       
>> This looks like a kernel problem to me. It's probably the Xserver asking
>> the kernel to set some memory range as WC but the kernel PAT code fails
>> to do so for some reason, it sets UC- minus instead (things should be
>> slower then).
>>     
>
> Things are veeeryyyy slooooowwww, indeed!
> It seems that the long-awaited xorg migration to testing caused my
> already slow video chipset to become even slower with OpenGL
> applications...   :-(
>   

Adding a WC MTRR manually might help. But you may have to boot with
"nopat" on the kernel command-line first since the WC MTRR is ignored if
the kernel sets UC- with PAT IIRC.

Brice