Re: Some considerations

On Wed, 2003-11-26 at 18:32, [email protected] wrote:
> I see your point now. Still, it might be better to keep them in AGP memory 
> anyway. You have to keep copying them over the AGP bus, but even at extremely 
> high drawing rates you can't be taking more than 100MB/sec. However, if you 
> want to be able to use the same glyph bitmaps for apps rendering to their 
> window buffer via software, you don't want to keep downloading them from video 
> memory. 

A note regarding AGP memory: On a lot of setups, it has to be uncached,
which means in lots of cases a very significant performance loss
(not all platforms, for example, have ways to enable write combining
on non-cacheable space)

One thing we can do is to dynamically bind user buffers in/out the AGP
space so that actual direct drawing to those happens as normal cacheable
memory, that gets cache-flushed when bound to the AGP space (I'm not
sure, but I _think_ Apple may do just that, that is dynamically
binding/unbinding user memory in the AGP space).

That works only if you don't write again to it once it's in AGP space,
or if you re-flush before the card has a chance to use it though.

Ben.