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Date: Thu, 23 Jul 2015 23:00:49 -0700
From: Tony Lindgren <tony@atomide.com>
To: NeilBrown <neilb@suse.com>
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Cc: Pavel Machek <pavel@ucw.cz>, "ksummit-discuss@lists.linuxfoundation.org"
	<ksummit-discuss@lists.linuxfoundation.org>,
	riverful.kim@samsung.com, kyungmin.park@samsung.com,
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	Bjorn Andersson <Bjorn.Andersson@sonymobile.com>
Subject: Re: [Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone
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* NeilBrown <neilb@suse.com> [150723 21:37]:
> On Thu, 23 Jul 2015 22:34:29 +0200 Pavel Machek <pavel@ucw.cz> wrote:
> > 
> > and the big one... for Android people (not me):
> > 
> > 6) do we need to use s2ram (and then pretend phone is not suspended)
> > to save power on cellphones? If so, do we need new interface for
> > applications to signal "I'd really like to run"?
> > 
> 
> For the first half of this question, the answer is:
>  Probably not.  runtime-pm should be able to put all devices to sleep,
>   and cgroup freezer should be able to freeze untrusted processes.

Yes s2ram is just an additional tool. PM runtime alone can
already provide a reasonable battery life for a phone as long as
it's properly implemented and the hardware supports it. With
reasonable battery life in this case I mean over 10 days in idle
mode with system running and timers working.

>  But I suspect runtime-pm doesn't provide as much power saving as
>  system suspend, and using the cgroup freezer means lots of changes to
>  userspace.
>  So lots of work would be needed to meet this goal, if it is a
>  worthwhile goal.

And with s2ram the difference is that then the system is not running
and timers don't work so it really needs to be optional.
 
> For the second half - it is really a user-space problem.  User-space
> decides when to enter suspend.
> (or CONFIG_PM_WAKELOCKS can enable a kernel interface
> via /sys/power/wake_lock).

Yeah agreed.

Regards,

Tony