Re: Question on BogoMIPS

Fire Dragon (
Mon, 14 Apr 1997 07:29:41 -0500 (CDT)

On Mon, 14 Apr 1997, Mike Jagdis wrote:

> > In the 2.0.27 and 2.0.29 kernels (RedHat distributed kernels with the
> > cyrix.pl2.patch file applied for the Cyrix CPU features) have given me a
> > BogoMIPS of 54.2 average while a 2.0.30 kernel that has only the cyrix
> > patch applied gets 99.2 BogoMIPS.
> >
> > I am confused on this as these three kernels are compiled exactly the same
> > would produce difference BogoMIPS for the same configuration options
> It sounds like branch prediction then. The Cyrix patches fiddle with
> the branch prediction settings - different patches do different

I think that patch does play with branch perdiction settings, but I would
have to take a look through it again to be sure.

I do know that I get aproximately the same results with and without the
cyrix patch applied which is strange...

> [...] With branch prediction,
> pipelining, speculative execution, register renaming and other bells
> and whistles the timing loop can make the bogomips value *completely*
> bogus (as opposed to merely misleading :-) ).

BogoMIPS invalid? never happens... must only be on those new fangled
MIPS machines where a BogoMIPS value would be invalid right?


Fire Dragon

A successful [software] tool is one that was used to do something undreamed of by its author. -- S. C. Johnson