[Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone
Tony Lindgren
tony at atomide.com
Fri Jul 24 06:00:49 UTC 2015
* NeilBrown <neilb at suse.com> [150723 21:37]:
> On Thu, 23 Jul 2015 22:34:29 +0200 Pavel Machek <pavel at 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
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