Re: Re: [RFC][PATCH -mm] PM: Introduce set_target method in pm_ops

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Hi,

On Monday, 25 June 2007 21:28, Pavel Machek wrote:
> Hi!
> 
> > >>> Right now the states we have are On, Standby, and Suspend, and the CPU
> > >>> runs only in the On state.  But on some platforms there could be
> > >>> multiple states in which the CPU is able to run, albeit with degraded 
> > >>> performance.
> > >> I wouldn't call those system sleep states.  For example, ACPI defines system
> > >> sleep states as the states in which no instructions are executed by any CPUs
> > >> and I think that's reasonable.
> > >
> > > Well, in some cases, we have 200MHz CPU running at 30kHz. ...that's so
> > > slow that it is pretty similar to ACPI sleep state.
> > > 									
> > Pavel,
> > 
> > let's do not mix the things. Rafael gave exact meaning of a sleep state --
> > "no instructions are executed by any CPUs", that, I assume, can be
> > interpreted
> > as "processor does not do any effective job". It does not mean if any clock
> > frequency supplied or not. In some cases the frequency supplied to speed up
> > the wakeup process, but, the processor can't operate on this frequency,
> > so this is a sleep state. But, if the processor can do some job,
> > even if a frequency very very slow, then this is an active mode.
> 
> Well, I'm trying to say that cpu (samsung arm in openmoko?) may be
> able to execute instructions at very very low speed, but that the
> speed is so low, that we should treat it as a sleep state.
> 
> I mean -- you can't use cpufreq to automatically chose between 32kHz
> and 200MHz.
> 
> ...but I guess it is all not too important...

Well, as I've just written to Dave, I think that we can define a 'system sleep
state' as a state that requires the main code path in kernel/power/main.c
(starting from enter_state()) to be executed in order for the system to enter
it.  Arguably, in such a state no useful work will be done by the system.

The other states can be regarded as 'running' or 'On' states.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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