Re: Re: Centrino speedstep

Fred Labrosse
2005-01-07T11:05:13Z

Dominik Brodowski writes:
> >
> > How can it not be the case that there is correlation between the two? The
> > processor produces heat
> Yes.
>
> > (less if throttling down, right?)
> Not necessarily. Only if the average CPU load would be higher than
> the rate the CPU is throttled to, i.e. if the CPU load is >= 100% for
> siginifcant amounts of time[*]. If not the CPU is put into the same hardware
> state ("idle state") because there is no work to do as if there were
> throttling, i.e. if "x" means the CPU has work to do, "i" means the CPU is
> in an idle mode, and "t" means the CPU is throttled, we see the following
> behaviour:
>
> Much work to do:
> -----------------------------------> time
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (no throttling)
> xxttxxttxxttxxttxxttxxttxxttxxttxxtt (throttling 50%)
>
> (however, as the task now takes twice as long to complete, and the CPU still
> consumes power in "t", the CPU does consume more energy than if it weren't
> throttled. Only if the fan needs to run _because_ of the high CPU load and
> it consumes more power than the CPU in throttling mode, throttling may save
> energy.)
>
> 50% load average
> xixixixixixixixixixixixixixixixixixi (no throttling)
> xxttxxttxxttxxttxxttxxttxxttxxttxxtt (throttling 50%)
> => as the CPU is in the same hardware state on "i" or "t", no power
> reduction is achieved because of throttling
>
> 10% load average
> xiiiiiiiiixiiiiiiiiixiiiiiiiiixiiii (no throttling)
> xittiittiittxittiittxittiittiittxit (throttling 50%)
> => the same is true again ==> throttling doesn't save you anything
>

I was missing something (brain power?). Very interesting. Thank you for
that.

> And as 100% CPU usage isn't that common on notebooks...

It is on mine... ;-).

Cheers,

Fred