Messages in this thread | | | Date | Sun, 16 Aug 1998 19:37:23 -0500 (CDT) | From | Oliver Xymoron <> | Subject | Re: Winmodem support, some performance tradeoff estimates |
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On Sun, 16 Aug 1998, Alan Cox wrote:
> > means the performance of using a soft modem is about 8 Pentium MHz, > > on the grounds that 1 32-bit Pentium MHz =~ 1 64-bit R4000 MHz in the > > Way off. Firstly Im dubious about the 8Mhz, secondly the R4K's tend to > have DSP instructions (ones that are useful). Pentiums dont have an > add/multiply with no stall instruction once per clock.
An unrolled multiply accumulate _can_ be done in 2 clocks per argument on a Pentium, however (hint: the fxchg instruction can be made to take 0(!!) clocks if ordered properly). I put together a signal processing app that did dot products at 45 mflops on a P90 last year. But this was only if its working set fit within the L1 cache.
With MMX, a 16-bit fixed point multiply accumulate could probably be done with about about a cycle per operand (multiply, shift, add, exchange) provided your vectors could be into four chunks large enough to unroll nicely.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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