945GM(E) screen rotation and slow GL.

Keith Packard keithp at keithp.com
Tue Jan 13 21:27:58 PST 2009

On Wed, 2009-01-14 at 13:18 +0800, Rob Kramer wrote:

> Cool, thanks. That's a lot better at 18 fps, but still a lot worse than
> normal landscape operation. Is that expected? I thought with modern GL
> setups, rotation basically came for free -- but I'm a GL newbie :)

The rotation is done by drawing to an upright frame buffer and then
copying that to the rotated frame buffer for presentation. That's a lot
of pixels to copy around each frame.

> Do you think the 945 chipset is just too slow to rotate a 1920x1200
> screen?

You're fairly seriously memory bandwidth limited with that chipset, and
at that resolution.

One thing that may improve performance a bit is when we get tiling
support for the displayed buffer. That work requires some additional
kernel infrastructure to manage the 'fence' registers which are
responsible for linearizing tiled regions for software rendering code.

You might try 16bpp instead of 32bpp; it won't look as good, but it
should go faster.

keith.packard at intel.com
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