cvs commit: src/usr.sbin/powerd powerd.c

[Bruno Ducrot]

On Mon, Aug 29, 2005 at 10:08:25PM -0700, Nate Lawson wrote:
> Bruno Ducrot wrote:
> >On Sun, Aug 28, 2005 at 10:36:38PM -0700, Nate Lawson wrote:
> >
> >>Another mitigating factor is a patch I hope to commit soon that removes 
> >>levels that aren't useful.  The general idea is the same as a recent 
> >>email from Tijl Coosemans but my approach is different.
> >
> >
> >I'm pretty sure it's incorrect to add p4tcc and acpi_throttle for power
> >saving purpose.  I plan to add some flags in order to use only relevant
> >frequencies to this end, but IMHO that should be done at low-level
> >drivers.  On the other hand, it is usefull to keep the existing sysctl
> >freqs, but for cooling purpose only.
> 
> I think throttling, whether via p4tcc or acpi_throttle, is a useful 
> addition to absolute frequency control (i.e. est or powernow).  With 
> appropriate tuning, as I hope the patch I committed provides, the 
> additional levels should be helpful.

Apart on older processors, I don't see the usefullness for power saving
purpose.  The problem is that when the processor is in stop grant state
in the duty cycle, it will consume more power than when it is in sleep
or deep sleep states (or deeper sleep state for some).
If the processor is idle, you will have nearly like 100% of time spend
in sleep state (for laptops) or stop grant state (for desktop), or even
better if the system support C3 etc.

But if you have a duty cycle of (say) 87.5% due to the idleness of the
system (and the result of powerd), then the processor will be put
for 87.5% of time in stop grant state which consume more power
than sleep state.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.