i915: FBO performance

Michel Dänzer michel at daenzer.net
Fri Oct 2 17:00:19 PDT 2009

On Fri, 2009-10-02 at 21:42 +0200, Thomas Zimmermann wrote: 
> Hi there,
> lately I've been playing around with OpenGL framebuffer objects while
> trying out shadow mapping with GL. The FBO is thereby used to render
> depth values to a texture, which is later needed for shadowing.
> When I attach renderbuffer objects or texture objects that have ~1000
> pixel per dimension to the framebuffer object, the framerate is ~160
> fps. However, in the range between 1009 to 1024 pixels per dimension,
> the performance drops to ~35 fps. For higher numbers of pixels (>=1025)
> the performance again goes up to ~160 fps.
> I've searched bugzilla and the ML archive for this, but haven't found
> anything. Also, the changelogs of the intel driver releases 2.8 and 2.9
> do not seem to contain any related entries.
> I'm on a system with a Core2 Duo x64-64, and an Intel 945 graphics chip.
> My distribution is an up-to-date Fedora 11, with Intel's xorg graphics
> driver 2.7.

See Mesa Git commit bcdaed2c0a4e70c3dd7c4648442c97540f3c9f1f:

	 /* XXX: At least the i915 seems very upset when the pitch is a multiple
	  * of 1024 and sometimes 512 bytes - performance can drop by several
	  * times. Go to the next multiple of 64 for now.
	 if (!(mt->pitch & 511))
	    mt->pitch += 64;

Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer

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