Re: suspend blockers & Android integration

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

>  - Create a 'deep idle' mode that suspends. This, if all constraints
>    are met, is triggered by the scheduler automatically: just like the other
>    idle modes are triggered currently. This approach fixes the wakeup
>    races because an incoming wakeup event will set need_resched() and
>    abort the suspend.
> 
>    ( This mode can even use the existing suspend code to bring stuff down,
>      therefore it also solves the pending timer problem and works even on
>      PC style x86. )

Note that this does not necessarily have to be implemented as 'execute suspend 
from the idle task' code: scheduling from the idle task, while can certainly 
be made to work, is a somewhat recursive concept that we might want to avoid 
for robustness reasons.

Instead, the 'deepest idle' (suspend) method could consist of a wakeup of a 
kernel thread (or of any of the existing kernel threads such as the migration 
thread) - which kernel thread then does a race-free suspend: it offlines all 
but one CPU [on platforms that need that] and then initiates the suspend - but 
aborts the attempt if there's any sign of wakeup activity.

Thanks,

	Ingo