Ian Romanick wrote:
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Tom Flynn wrote:
I'm CC'ing mesa3d-dev because that's where most of the 3D specific work
is discussed.
I have couple quick questions about Unichrome Pro. A couple months ago, I
was trying out a Unichrome Pro based machine. I'm not sure if things have
changed since then, but there was two major things that turned me off of
it....
1) max texture size was 512. is this a limitation of the chip or of the
driver? if this is a limitation of the driver, what needs to be done to fix
it?
Most likely a limitation of the amount of available texture memory. The
3D driver will only report texture sizes that it can be sure will fit in
texture memory. If it can't fit a 1024x1024x24-bit texture for each
texture unit (2 on Unichrome), it will only advertise 512x512.
Also a limitation on the number of mipmaps the hardware will correctly support.
I believe the patch in the bugtracker simply enables incorrect behaviour, so
isn't really a candidate for inclusion.
2) texture download performance was pretty bad. looking in via_tex.c, it
looks as if it does a memcpy to update the texture. the via_sse_memcpy was a
little faster, but still not nearly fast enough. is there a faster way?
(dma?) Or is there some limitation due to how the driver is written? I
noticed the open-source radeon driver was just as slow. The closed source
ati drivers were several orders of magnitude faster.
Keith Whitwell did some work in that area not too long ago. You might
want to touch bases with him.
It's worth putting the work into understanding why the SSE memcpy routine was
failing for some people - I saw a speedup of >50% on testing here with that path.
I think it's actually pretty good that the via driver matches the radeon's
texture upload performance - a direct-copy upload is matching the performance of
a dma upload on (I'm guessing) a more capable machine. Was the test on the same
machine? Do unichrome systems with agp slots exist?
The ways to faster upload performance on unichrome would seem to be:
1) explore the dma work that has been done recently in the X11 driver and
see if that can be brought over for texture uploads.
2) investigate the technique of uploading by pulling texture data into the
GTT without performing any copying.
Probably (2) is what you're looking for, but there are no open-source examples
of how to do this. Kudos will await if you figure it out & implment a workable
scheme - it's mainly a matter of kernel hacking, I don't think the hardware
issues are particularly difficult.
It's worth noting that the unichrome is not a radeon, and the cpu's on those
boxes are quite constrained compared to fast P4's and Athlons. This will have
an effect on how far you can take this.
Keith
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