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Bug#542701: xserver-xorg-video-intel: Very slow 2D performance on one screen of dual display until after switch to console VT and back.



Excerpts from Thomas Vaughan's message of Wed Aug 26 11:57:59 -0700 2009:
> At 2560x1024 and 3200x1200, the initial condition is for the right
> monitor to be slow for 2D and 3D.
> 
> After I do a VT switch via CTRL-ALT-F1 and back (ALT-F7), both 2D and 3D
> are fully accelerated on the right monitor, at 2560x1024 and at
> 3200x1200.

Hi Thomas,

You've got a very mysterious bug.

The acceleration code in the driver isn't aware of the two different
monitors at all, (it's just seeing coordinates).

I discussed the problem with a room full of graphics engineers and
mostly got head scratching. But there was one germ of an idea: Perhaps
there's some odd RandR transformation being configured for the one
display. (For example, imagine the code going through an extra copy
and transformation as if rotated.) Something like that might cause the
slowdown. And doing the VT switch might get your desktop environment
to reconfigure the RandR stuff correctly the second time.

That's not much of a theory, but you might poke around to see if the
output of "xrandr" changes from before to after the VT switch. You
might also try running with a different desktop environment (or none
at all) to see if the buggy behavior changes at all.

-Carl



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