The Official NVIDIA G80 Architecture Thread

There's a fair number of niggly errors, definitely v1.0-itis, but still very readable.

Jawed

 

Anyone noted these quite moderate occlusion results:

 

Those numbers (I'm guessing which you mean, since they aren't actually showing) on their own don't seem to mean much as far as I can tell.

I do wonder, though, if this might be why G7x is so poor at Oblivion's foliage?

Jawed

 

Err, isn't it 8 quads to a batch?

Can it reorder batch elements on the fly? I believe Chalnoth threw that out, and with 2x16 it ought to be *possible* (though complex) to swap a single 16 section around. I suppose the test for that is fairly simple -- two consecutive branches corresponding to, say, even 16x2 regions and odd 16x2 regions, respectively. I wouldn't expect it to manage that, but it would be cute if it did.

Is the 32 batch size dictated by 8 texture units x 4 color components? That would seem to imply vector instructions issued wide, rather than serialized, which seems incredibly unlikely to me. Or is there something important about keeping a single texture unit across a whole quad? /me lost

 

HSR speed can be determined quite accurately from Humus' GL_EXT_reme benchmark. Just subtract the render times (i.e. 1/fps) between the 8x overdraw and 3x overdraw (front to back) and multiply by the core clock. Then divide 5 times the screen res by that number and you get the rejection rate per clock.

I've found it works really since R300, maybe even earlier.

 

Because branching doesn't work like we want under GLSL with ATI... They try to unroll loops and predicate branches in all public drivers. We have DX versions of the test, they used to behave, but there was a subtle change in the DX spec that is breaking the test for *both* vendors, so we need to figure out how to fix that...

 

I believe the attribute interpolation is one channel per clock, for four pixels at a time. So the duration of the interpolation corresponds with the number of channels defined for the attribute.

http://www.beyond3d.com/forum/showpost.php?p=869366&postcount=49

Jawed

 

Isn’t this the logical result of having scalar units?

 

Yeah - but I'm not convinced Uttar is thinking through the rates correctly.

There are 16 attribute interpolation "pipes", but only 4 SF pipes per cluster. 4 interpolation pipes are ganged per SF pipe.

Jawed

 

If you look up so many gradients, why not precompute them into a second volume texture?

 

One question:
Pixel shaders work in quads, but vertex shaders don't. Does this mean that the "special functions" will be 4 times more expensive when used in vertex shader than in pixel shader?

 

No, they will not.

 

Tell me about it, just something else, if the g80 was planned for last year, what else does nV have planned?

 

I invested the time a few weeks back

Agreed. Actually, to be fair, it's Rys's diagram:

http://www.beyond3d.com/reviews/nvidia/g80-arch/image.php?img=images/g80-diag-full.png

which I think may be confusing things, at "10". The SF and interpolation rate is the same (i.e. the pipeline is equal in length for both), but it's the 3 auxilliary paths dedicated to interpolation that result in the 4x multiplier - rather than SF's taking 4x longer to compute.

It's clearer to think of 4 quad dedicated interpolation pipes, with each quad dependent upon a single SF pipe.

Yeah.

Jawed

 

Vista's release date has been pushed way, way back. ATI and NVidia should both have been planning on releasing something a long while back. What they've each done with the extra time, who knows?...

It's also worth pondering how recently stuff was last added into (or more likely) taken out of D3D10.

Jawed

 

True, but if ATi is 4 months behind right now, I don't think we have to look to far to see where they were along the way, if nV's problem was due to chip size. Which in all honesty doesn't really make much sense to me if it was chip size that means yeilds of the g71 weren't as good as nV was saying orginally.......

But that doesn't make much sense either because thier net profits are threw the roof even with the increased recall numbers.

 

What errors have you spotted?