Re: 3DNow! patches on Winchip.

Alan Cox (alan@lxorguk.ukuu.org.uk)
Thu, 30 Dec 1999 13:43:07 +0000 (GMT)

> From some preliminary benchmarks I just conducted on my Winchip 2A-233,
> Using 3dNow/MMX memcpy is a around 7-8 times faster than a plain
> memcpy. This is however running on a 66Mhz bus, and the chip is designed
> for running on a 100Mhz bus, so the real gain is probably much higher.
> (I don't have a 100Mhz board to test this).
>
> My initial thought, is to add an 'IDT Winchip' option to the CPU selection
> menu of the config, which then sets the CONFIG_X86_USE_3DNOW
>
> Comments?

Make sure you benchmark both the cached and uncached cases. If it is definitely
a win to use the 3dnow code then use it. Note that there is some stuff
pending (hopefully for 2.4.0) that allows you to plug in multiple memcpy
routines and handle the choice per cpu. That will also allow you to do
finer tuning for the winchip. Right now with the current draft of that code
it has support for

Integer copies (rep movs etc)
MMX + 3Dnow! (mmx with prefetch)
MMX no 3dnow (older mmx cpus)
FPU trick (earlier preventiums)

and more can be added (eg the K6-2 seems to be fastest using integer operations
unrolled, and with prefetch stuff)

Alan

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