suspend/resume PM criterion for application

[Valdis.Kletnieks at vt.edu]

On Wed, 10 Sep 2014 20:26:48 +0300, Ran Shalit said:

> What is usually the criterion for PM (power management) suspending
> that application shall use ? Is it according to minimum threshold for
> cpu load (as indication for no process) ?

That will be highly application dependent.  Something that checks your email
in the background may not care at all, as long as it gets network
access every 5 minutes or so, and the entire system can power down for 4 minutes
and 58 seconds as far as it cares.  If it's doing media streaming, it may
insist on having at least one CPU burst per screen refresh, and the CPU can
go to sleep for the rest of the 1/30th of  a second.

> How usually it is performed, i.e.  is it some periodic process, which
> wakes up periodically to check criterion for cpu load ? If so, isn't
> it problematic in PM terms, becuase it mean that the system is resumed
> periodically (as a result of the the periodic timer's interrupt), and
> all devices are resumed ?

No, it can be done on a per-device basis.

'powertop' is a possibly useful tool for playing with this stuff that will
let you look at power management on the fly.
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