Re: your mail

Rocke Verser (rcv@dopey.verser.frii.com)
Tue, 15 Apr 1997 16:07:49 -0600


> From: rrt0136@ibm.net (Ronald Van Iwaarden)

> I am curious as to whether a generic
> optimized version might work better on the Cyrix platform.

Ron and other Cyrix users:

The "486" optimization is essentially a "generic" assembly version.
I can almost guarantee that the non-assembly code generated right out
of the C compiler would perform 1/3 to 1/2 less well.

The "P5" version is optimized to make maximum use of the dual
instruction pipes. This code is so highly honed that it is executing
about 375 machine instructions in 200 clock cycles.

The "P6" version is optimized for the multiple uop queues, and also
to minimize "stalls". "Stalls" are very costly to the P6.

The keycrunching code contains no floating point operations.

> This is terrible performance for the Cyrix which usually
> performs at the same speed as an Intel P150 unless intense FP is used.

I don't know the architecture of the various Cyrix chips. If they
have a single instruction queue, you should expect performance no
better than about half of a Pentium of the same speed.

If it is highly subject to "stalls", or if they are especially costly,
you should expect even less.

Someone else has stated on this list that a Cyrix 586 is really a
486-class processor. I don't know.

-- Rocke