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SubjectRe: [PATCH 0/8] Suspend block api (version 7)
From
2010/5/18 Kevin Hilman <khilman@deeprootsystems.com>:
> Arve Hjønnevåg <arve@android.com> writes:
>
>>
>> PM: Opportunistic suspend support.
>>
>> Power management features present in the current mainline kernel are
>> insufficient to get maximum possible energy savings on some platforms,
>> such as Android, because low power states can only safely be entered
>> from idle.  Suspend, in its current form, cannot be used, since wakeup
>> events that occur right after initiating suspend will not be processed
>> until another possibly unrelated event wake up the system again.
>
> I think the problems with wakeups in the current suspend path need to
> be described in more detail.  In particular, why check_wakeup_irqs()
> is not enough etc.
>

check_wakeup_irqs only handles interrupts that occurred after the
interrupt was masked during suspend. If the interrupt occurred before
it was masked, it will not be pending when check_wakeup_irqs is
called.

>> On some systems idle combined with runtime PM can enter the same power
>> state as suspend, but periodic wakeups increase the average power
>> consumption. Suspending the system also reduces the harm caused by
>> apps that never go idle. On other systems suspend can enter a much
>> lower power state than idle.
>>
>> To allow Android and similar platforms to save more energy than they
>> currently can save using the mainline kernel, we introduce a mechanism
>> by which the system is automatically suspended (i.e. put into a
>> system-wide sleep state) whenever it's not doing useful work, called
>> opportunistic suspend.
>
> A definition of "useful work" here would provide clarity and would
> also help clarify by what criteria other on-going work is determined
> to be not useful.
>
> Kevin
>



--
Arve Hjønnevåg
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