Re: [Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Thursday, July 23, 2015 11:00:49 PM Tony Lindgren wrote:
> * 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.

Right.

Even with suspend-to-idle we can get less energy usage with respect to
runtime idle (device runtime PM plus cpuidle) just because timer events
are disabled then.

> > 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.

Right.

Thanks,
Rafael