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SubjectRe: suspend blockers & Android integration
On Fri, 4 Jun 2010, Ingo Molnar wrote:

> 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.

Out of morbid curiosity... A typical sign of wakeup activity is a
thread becoming runnable because of expiration of a kernel timer or an
I/O completion interrupt. How would the "race-free suspend" thread
detect this sort of thing? Indeed, isn't the inability to detect these
part of what makes the existing suspend implementation (the freezer in
particular) not race-free?

Alan Stern



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