cpufreq governor vs. powernowd

[John Richard Moser]

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Paul Sladen wrote:
> On Fri, 18 Aug 2006, Aigars Mahinovs wrote:
>> On 8/18/06, Dmitriy Kropivnitskiy <nigde at mitechki.net> wrote:
>>> 1. Remove powernowd from the default install
>> would be nicer to have powernowd doing its magic when the laptop is on
>> battery (it does increase the battery life quite significantly), 
> 
> Are you able to help come up with a harness for collecting some real-world
> results on this, there are various other factors, such as the additional CPU
> time and 'powernowd' consumes from running itself;  and ideally we need to
> be able to take all of these into account.
> 

Logically, the additional CPU time is probably not an issue.  The issue
is probably that powernowd is a user process that has to figure out what
the CPU is up to; meaning the kernel has to tell it it can run before it
can take a sample.  Then it has to make changes to the kernel
configuration (i.e. up the CPU clock).  I could see this getting blocked
for a few mS under load, whereas the kernel might notice it faster.

I don't know the innards of the kernel though.  It seems logical to me
that the kernel could recognize that of the past X time slices, N were
used fully, and so the CPU is [not] under load now; or just directly
have the process scheduler watch how much the idle loop has run the past
few jiffies and switch during scheduling.  I can't, however, say that
that's how it's done.

> 	-Paul

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