From: Alex Jackson <awj_in_japan@ho...> - 2006-12-05 00:27:02
I've just noticed that setting my AGP transfer speed (via BIOS setup) to 4x
rather than 8x results in *faster* framerates in OpenGL apps with my Radeon
9200SE. The speed difference is a nearly constant 20% across the board,
regardless of what OpenGL functionality the app uses:
AGP 4x: ~1900 FPS
AGP 8x: ~1500 FPS
sdlmame (unthrottled, running pacman):
AGP 4x: ~1100 FPS
AGP 8x: ~900 FPS
Note that these two apps are pretty much at two opposite ends of OpenGL
usage: glxgears is all geometry and no textures, while sdlmame is doing
nothing but continuously uploading a large texture and rendering it parallel
to the screen.
I've looked in /var/log/messages and /var/log/Xorg.0.log and it looks like
both AGP modes really are using the mode I select; neither is failing and
falling back to a slower mode. I'm running stock FC5 with all updates.
Does anyone have any idea why AGP 8x yields worse performance than 4x? Does
this happen to other people with rv280-based cards (the only chip in the
r200 family that supports AGP 8x)?
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