Power Management

[Richard Hughes]

On Fri, 2007-06-08 at 11:42 -0400, Chris Ball wrote:
> Hi,
> 
>    > Is there a mechanism for either applications or users to change the
>    > parameters? And what constitutes "idle"?
> 
> A first shot at what constitues "idle" is if all of the below are true:
> 
>    * if the CPU isn't under load

Which we can get from the system load, or is there a better geode
specific way of doing this?

>    * if the video on the screen isn't changing

How can we get this from userspace?

>    * if we aren't dealing with any keypresses/input from the user

We can monitor input devices...

>    * if the currently running activity hasn't told sugar/OHM to inhibit
>      sleeping while it's running

Like when?

>    * if there isn't a software tick (dynticks/tickless) planned for the
>      very near future

Can we get this info from the kernel?

>    * .. then we can go to sleep.  :)

Finally! :-)

>    > Similarly, turn-based games over the mesh might have you waiting
>    > while your opponent moves, and you might not be sitting there
>    > tapping the keyboard while waiting.
> 
> This should be fine -- when your opponent's move's network traffic hits
> the Marvell chip, it will assert a wakeup and the CPU'll come back and
> process the traffic.

That's some pretty sweet hardware.

> I'm actually having trouble thinking of a case where we want to inhibit
> suspend that isn't already inhibited by the heuristic above.  Can anyone
> else?  Richard mentioned "don't suspend during a system update", but
> if our system update tool breaks the system when we run out of battery
> in the middle of an update, we have bigger problems.  The tool should
> operate atomically if it can.

Surely you don't want to suspend during a system update or software
installation... We can even use the HAL lock interface to do this.

Richard.