twitching image

Alex Deucher alexdeucher at
Mon Sep 14 07:02:37 PDT 2009

On Sun, Sep 13, 2009 at 9:27 PM, Csillag
Kristof<csillag.kristof at> wrote:
> Alex Deucher wrote:
>> This is likely display watermark or pll related.
> What is a display watermark?

All of the memory clients on the GPU (display controllers, 2D, 3D,
overlays, etc.) contend for memory bandwidth from the memory
controller.  If the display controllers are starved, you end up with
underflow which can manifest as sparkling or blanking of the display
at certain times.  To avoid this, you need to properly set up the
display fifos and priority levels.  This tends to be more evident on
DVI since the signal is digital.  Also, IGP chips are more prone to
watermark problems since they are sharing memory bandwidth with the
rest of the system.

>> Please try xf86-video-ati from git master as that has proper watermark setup
>> implemented and support for fractional feedback dividers.
> I will do this tomorrow; just one question until then:
> if this has anything to do with the driver,
> then how is it possible that the frequency of the problem
> can be influenced by changing the DVI cabling I use?

low quality DVI cables can causes problems, but if the same cable
works on other systems, it's probably driver related.

>> If you are still having problems with master, please try:
>> Option "DisplayPriority" "HIGH"
>> in the device section of your config.
> I have already tried that, and it did not help.

You need git master.


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