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SubjectRe: BogoMIPS revisitied...MMX
On Tue, 17 Mar 1998, George Bonser wrote:

> Here is an interesting array:
>
> AMD K5-100: 199.07 BMPS
> INTEL P-60: 23.96 BMPS
> Cryix 6x86 P150+ (at 120MHz): 52.33 BMPS
> INTEL 486-DX266: 33.08 BMPS.
>
> Why is the AMD 100MHz CPU 4x faster (in BogoMIPS) than a Cyrix running a
> 20% higher clock speed? I would say that the AMD CPU Microcode is
> optimized more toward the type of instruction that the bogomips loop
> executes. Why is it nearly 10x faster than the Intel chip?

I guess the AMD is better optimised for an empty loop. I have the
feeling that the 6x86 only does branches in the X pipeline. If the
AMD does them in both pipelines the difference in an empty loop
could be a substantial part of the total. The 486 simply doesn't
have the pipelining, register renaming, branch prediction etc.
so I wouldn't expect high numbers. The P60 is similarly, but not
as comprehensively, held back.

> I dunno, but I think I will buy more AMD chips ;)

Huh? You want to run empty loops? If you don't know why you see a
difference in a very specialized piece of code you shouldn't
assume the difference scales to general code. *Everyone* optimises
for the common benchmarking code. But this is only good if you
want to run benchmarks fast :-).

Mike

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