[maemo-developers] Internet Tablet Power Management presentation from linux-pm summit 2007

[From: Igor Stoppa]

On Wed, 2007-07-11 at 14:29 +0200, ext Frantisek Dufka wrote:
> Igor Stoppa wrote:
> > I certainly will run my tablet at higher speed and/or lower voltage;
> > finland makes it unlikely to incur in heating problems ;-)
> 
> CPU temperature sensor might be useful to guess the limit and cut the 
> speed down in case one is not in Finland :-) Is there one?

There is one between omap and the combo chip memory, but it is quite
sucky. Not that we haven't thought about it.

If there is some spare time (yeah, right) we could try to use it, but TI
is unlikely to support it and therefore i'm quite confident it will ever
ship (albeit it would be quite interesting since it would allow much
more aggressive trimming down of the voltage).

> Well, I'm not sure but maybe when being conservative with power saving 
> and when some hints are applied (i.e some API) it could work. I'm mainly 
> thinking about CPU spikes when applications are starting. I fear the 
> system will not react quickly enough with 'overclocking' when 
> application starts since otherwise the device does nothing before and 
> after. But this specific problem could be solved with some hints done 
> from application launcher or maybe kernel or libc (exec/fork call) itself.

Ondemand starts by cranking up to the max the frequency. It cannot be
beaten.

> I'm not sure how linux currently does it on x86 (shame on me, using XP 
> on laptop and linux only in vmware) but my experience with RMClock on XP 
> (http://cpu.rightmark.org/products/rmclock.shtml) is that it is 
> hard/impossible to tune it in such way that application startup is not 
> slower and you still save some power.

OMAP has retention so it's not that critical to fine tune. x86 otoh
doesn't, afaik, so it would require more aggressive tuning

[snip]

> > You mean QoS. Yes, that seems to be the general understanding.
> 
> Yes that's it. Didn't know this term is used also in power management, 
> though.

I use it :-P others are more shy about it, but when asked they admit
that it is what they have on their mind.

-- 
Cheers, Igor

Igor Stoppa <igor.stoppa at nokia.com>
(Nokia Multimedia - CP - OSSO / Helsinki, Finland)