On 30 Dec 2001, Owen Taylor wrote:
> [2] Right now, to get decent performance, the source must be
> in system memory - we clearly need this for decent performance
> for the software fallback, and XAA also only supports this.
> For the local rendering case, we can enforce the source
> being in the right place by using a ShmPixmap. For the
> remote case, we have no way to enforce this, and given
> sufficient video ram, we'll get bad performance.
It wouldn't be too difficult to force sources out of video ram
when they are used in composite operations. I do that for other
cases such as offscreen pixmaps being used as tiles in GCs used
on system memory pixmaps.
Yes, XAA assumes all data is in system memory and doesn't
optimize when both source and destination are in video ram, which
should be the fastest case of all. The drivers can hook this
high enough to do this themselves, but XAA doesn't have low-level
functions to do this. I can add this to NVIDIA's drivers easily
enough, but the problem is testing. I've hardly seen anything
resembling a test or performance suite for Render. I can't accelerate
anything I can't test, which is why XAA will only accelerate some
very simple cases.
Mark.
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