linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902170026.06966.rjw@sisk.pl>
Date:	Tue, 17 Feb 2009 00:26:05 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@...e.cz>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Arve Hj?nnev?g" <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Monday 16 February 2009, Pavel Machek wrote:
> Hi!
> 
> > The recent descussion about the Android PM patches sent by Arve shows that
> > there is a need to introduce a mechanism allowing us to:
> > (1) automatically put the system as a whole into a sleep state (eg. suspend to
> >     RAM) when it is found to be "idle", where the meaning of "idle" has to be
> >     defined too,
> 
> Well; I'd prefer to keep the interface very minimal.
> 
> If no devices are being used,

We'll need some kind of infrastructure to detect such situations.

> and next wakeup is far enough in the future,

What exactly do you mean by "next wakeup"?

> just put system to sleep.  Long enough == so far away that suspend/wakeup
> is short compared to that... like 20 seconds on PC.

Well 10s will be fine on the majority of my test boxes, but that's a detail.

> Ok, it probably needs to be opt-in: echo auto-mem > /sys/power/state
> should do the trick.

Agreed.

> This will need either fixing all the applications not to poll, or
> maybe someone SIGSTOP-ing apps that are in background and poll too
> often.

Polling in general is not PM-friendly, so we'll need to deal with it somehow
at one point anyway.

Thanks,
Rafael
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