BogoMIPS (Re: [plug] Bogus Sound Card Problems)

[Anthony J. Breeds-Taurima]

On Fri, 4 Aug 2000 bburns at erggroup.com wrote:

> 
> 
> Matt Kemner eloquently stated :
> 
> > On Fri, 4 Aug 2000 bburns at erggroup.com wrote:
> 
> > > G'day Pluggers,
> > >
> > > First a question:  What is a Bogomip - specifically, how is it calculated
> and
> > > what is it meant to represent?  It seemed to jump a whole heap (5 times)
> after
> > > installing a later kernel on the same machine.  Is it Bogus?
> >
> > Yes :)
> >
> > It is just an internal timing loop, which can fluctuate between different
> > kernel versions, and will fluctuate between different CPUs.
> >
> > >From the BogoMIPS mini-HOWTO:
> > (which will be available somewhere on http://www.linux.org.au/LDP/HOWTO/
> >  when someone kicks the webserver back into gear)
> >
> >  `MIPS is short for Millions of Instructions Per Second.  It
> >       is a measure for the computation speed of a program.  Like
> >       most such measures, it is more often abused than used prop
> >       erly (it is very difficult to justly compare MIPS for dif
> .       ferent kinds of computers).
> >
> >       BogoMips are Linus's invention. The kernel (or was it a
> >       device driver?) needs a timing loop (the time is too short
> >       and/or needs to be too exact for a non-busy-loop method of
> >       waiting), which must be calibrated to the processor speed of
> >       the machine. Hence, the kernel measures at boot time how
> >       fast a certain kind of busy loop runs on a computer. "Bogo"
> >       comes from "bogus", i.e, something which is a fake. Hence,
> >       the BogoMips value gives some indication of the processor
> >       speed, but it is way too unscientific to be called anything
> >       but BogoMips.
> >
> >       The reasons (there are two) it is printed during bootup is
> >       that a) it is slightly useful for debugging and for checking
> >       that the computers caches and turbo button work, and b)
> >       Linus loves to chuckle when he sees confused people on the
> >       news.'
> 
> Seems that if it can go from 66 to 330, just by upgrading the kernel (and not
> ending up with 5 times speed increase for real applications), that it is a
> "little" unreliable.

Not unreliable from a software point of view.  If the kernel calculates the
bogomips and then uses it the, value is arbitrary to you and me.  As long as 
the value remains ture for that boot then they dont matter.  (There was a nasty
problmem with toshiba notebooks, CPU's and power.  Thats another story.)

The reason you saw a jump was some where arround 2.2.13 Alan Cox changed the
way it was calculated.  which resulted in a vastly differnt number.

Yours Tony.

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