Re: CyrixInstead ?

Andrew Derrick Balsa (
Fri, 31 Jul 1998 22:27:10 +0200

Hi Rob,

On Wed, 29 Jul 1998, Rob Dale wrote:
>Hmm.. What's the recommended setting for a K6?
>I always compile as 486. :)

You would probably prefer to compile the kernel as a Pentium or PPro.

The only difference between the Pentium and PPro compile options is in the
string operations (AFAIK). The Pentium option uses a header file that
disassembles the complex string opcodes into simpler, but slightly faster

The PPro option uses the complex opcodes, but should be slightly faster than a
Pentium. I think the same rules apply to the 6x86 family and the K5/K6, but the
difference in speed is minimal between the Pentium and PPro kernel config
options on these CPUs (PPro should be slightly better).

OTOH the 486 kernel config option should _not_ be used for anything above a
486-class CPU. It sets alignment options that work well on the 486, but that
cause excessive padding on 586 and above class machines. Usually, the 6x86
speculative execution capabilities will just optimize this padding at run time,
but the NOPS still take precious cache space (same should apply to the K6; I am
not 100% sure of what the K5 does).

All the above remarks apply to 2.0.x kernels. I am not current on 2.1.x
kernel code. Please correct if I am missing something.

Hmmm, perhaps this should go in the FAQ? I have seen this question asked a few
times already...


Andrew D. Balsa

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