Re: Performance

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Angus Dorbie (dorbie++at++sgi.com)
Mon, 20 Jul 1998 13:57:29 -0700

Jeffry J Brickley wrote:
>
> We're looking at buying new hardware based on SGI's latest
> Graphics Architecture, and I brought up the wonderful question that our
> salesman could not answer.... Has anyone made a quantitative performance
> review of adding system memory and it's affect on Virtual ClipMap
> support? We are going from the first Onyx Infinite Reality with only 1
> Gig of memory, we're looking at 2Gig or more, but are unsure of where the
> performance break is.... Although I'm sure that our salesman would
> prefere the highest amount of memory we can imagine, I'm not sure our
> pocket books can survive that number.... As far as size of ClipMap goes,
> chances are we are going to pick as large of a ClipMap as our hardware
> can handle.... Imagery is not a problem, we can probably get more imagery
> than the disks/system could support.
>
> Jeffry J. Brickley <jbrickley++at++programmer.net>
> SRS Technologies
> White Sands Missile Range, NM
>
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The point of CLIP maps is you have lot's of immagery on disk rather than
in system memory and in system memory rather than texture RAM.

It depends on the texel size, tile size, the clip size region and the
number of virtual levels (although instantaneous levels in tram is
limted, you'll want all levels in system memory). Each CLIP region
should be padded by at least two disk tiles on each axis (one all
around) and probably more, this can depending on your CLIP centering
strategy.

You can do some simple arithmetic based on your data requirements but
I'd say spend your cash on big fast disk arrays. Get some big Ciprico
fiberchannel drives. You won't need an extra gigabyte for CLIP texture
and you should have enough memory with two or three hundred MB to store
and pad the CLIP region. The thing to ensure is that you have the
bandwidth from the file system to page the CLIP map tiles fast enough,
and disk space is cheaper than RAM.

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


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