Re: dynamic-hz

Zwane Mwaikambo
2004-12-13T15:31:16Z

Hi Russell,

On Mon, 13 Dec 2004, Russell King wrote:

> This is an easy thing to grab hold of, but rather pointless in the
> overall scheme of things. Those of us who have done power usage
> measurements know this already.
>
> The only case where this really makes sense is where the CPU power
> usage outweighs the power consumption of all other peripherals by
> at least an order of magnitude such that the rest of the system is
> insignificant compared to the CPU power.
>
> Note: the above CPU power consumption figures were taken from
> the Intel PXA255 processor electrical specifications, and the
> "rest of the system" current consumption taken from a real life
> device. The timer interrupt taking 2us is probably an over-
> estimation. Only the battery lifetime of 24 hours is ficticious.

While i do not disagree with your research and resultant conclusions for
the PXA255 processor i think it may not be as representative of some of
the target systems we're interested in, that is, x86 (cringe, cringe). A
number of i386 systems enter model defined partial suspend states when
execution of the hlt instruction takes place, resuming from these suspend
states draws more power for a short period of time thus doing this every
millisecond is going to be detrimental to total power consumption over
time. But this isn't only an i386 trait as other desktop/workstation
processors are similar.