Re: Toward runtime power management in Linux

["Jordan Crouse" <jordan.crouse@amd.com>]

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> > 	This could potentially make performance-conscious apps "hiccup"
> > once every second as this thread goes walking the list looking for
> > candidates to shut off.  Try to avoid this; if nothing is happening, nothing
> > should be running.
> 
> I don't understand this comment at all.  Lots of things happen 
> periodically in the kernel: threads wake up, timers go off...  Are you 
> suggesting that, for example, the page-flush thread shouldn't wake up 
> from time to time either?

While I don't agree that it will be a horrible drain on performance, I do
see a large potential for abuse with a big kernel thread.  Things like the
page-flush thread are well known and (hopefully) optimized entities -
the RTPM thread will have to depend on hundreds of driver writers to be kind
to not suck time and resources from the system.  About the time that somebody
puts a large udelay into their AC97 driver to turn off the DAC, then I'm sure
we will question our motives in this regard.

That said, I think I tend to favor the big kernel thread, or at least timeout
threads on a bus level.  The single entity handling the idle math timeout
would facilitate future issues such as priority in handling idle timeouts 
(do we address certain buses/devices before others, for example), plus it
would help centralize the functionality, and make it easier to control with
any future power management policy concepts.

Jordan

-- 
Jordan Crouse
Senior Linux Engineer
AMD - Personal Connectivity Solutions Group
<www.amd.com/embeddedprocessors>


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