linux-kernel - Re: [RFD] Automatic suspend

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Date:	Tue, 17 Feb 2009 21:35:02 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	"Woodruff, Richard" <r-woodruff2@...com>
Cc:	Brian Swetland <swetland@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Pavel Machek <pavel@....cz>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Len Brown <lenb@...nel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [RFD] Automatic suspend

On Tue, 17 Feb 2009 18:18:59 -0600
"Woodruff, Richard" <r-woodruff2@...com> wrote:

> > On Tue, 17 Feb 2009 09:32:46 -0600
> > "Woodruff, Richard" <r-woodruff2@...com> wrote:
> >
> > > > so use range timers / timer slack for those apps that you do not
> > > > trust. That is not a big deal, and solves the issue of timer
> > > > wakeups...
> > >
> > > I not so sure it is that straight forward in practice.  End
> > > systems integrate a lot of 3rd party software who view
> > > performance 1st and have no thought of power.
> >
> > you know that with the range timers/slack, you can control the
> > "rounding" of the timer of the application, right?
> 
> I've not explored user space for this.
> 
> Can on a per-application basis some controlling application cause
> timers of a target process to be rounded or is it global?

it is actually per thread.. so rather fine grained
 
>Or do you
> need to link the new application to use special glib variants (as
> described in OLS papers a few years ago)?

no you can do it for 100% existing binary

> 
> Your change here does look like something which could be used to
> control timers.  Don't you still need some dynamic way to set the
> fuzz/slack if its globally applied?  It seems like you might want
> some timers precise and others fuzzy.

right now it's prctl() based. We have been looking for a good use case
for making it per syscall.. but haven't found a convincing one yet.

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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