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SubjectRe: suspend blockers & Android integration

* 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


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