Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

[Mike Chan]

On Thu, May 27, 2010 at 5:05 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> On Friday 28 May 2010, Alan Cox wrote:
>> > The approach with user space power manager suggested by Dmitry and Alan Stern
>> > may work, but it still assumes some kind of suspend blockers to be present in
>> > the kernel.  If we reject that too, I wonder what approach Google is supposed
>> > to use and still get the same battery life they get with suspend blockers.
>>
>> I'm getting less convinced it needs suspend blockers at all for this case,
>> assuming that you are willing to have a policy that is based on
>>
>> - assuming apps play nicely
>> - having the information to user space you need (who woke us, who blocked
>>   us, events)
>> - dealing with offenders primarily from user space using that information
>>
>> I'm fairly happy about the following so far
>>
>> - we should have a common interface for seeing some pm events (like
>>   duh ?) but it does need careful thought so the watcher doesn't change
>>   the behaviour and break it. (Message "We are suspending", gosh someone
>>   is running to receive the message, resume being the obvious case)
>>
>> - Suspend is (for many platforms) just a cotinuation down the power
>>   chain. Demonstrated and implemented on ARM. Very much the direction of
>>   S0i1/S0i3 on x86 MID devices. Proved by the fact it has been done and
>>   made to work, and by reading the Moorestown PR.
>>
>> - Given a non forced (that is 'idle down') transition to a suspend level
>>   we can implement a 'suspend as idle' on many embedded platforms in a
>>   manner which is not racy at kernel level. Apparently implemented
>>   already on ARM
>>
>> - Given a non forced transition to such a suspend level and the reporting
>>   of certain events we can do a full user space managed graphical UI type
>>   environment policy in a race free fashion
>>
>> - With notification of who caused a resume and maybe a bit of other
>>   general stat gathering it is possible to identify and handle abuses of
>>   power resource. Proved by the fact we can do this with powertop but
>>   more elegance in the interfaces would be nice.
>>
>> I am not sure if a pm event is what is needed for this or a sum 'hardware
>> triggered wake up' event.
>>
>> I accept that current ACPI based laptops probably couldn't make use of
>> such a feature but I don't think this is important at the moment.
>
> No, it's not.
>
>> A resource constraint model might help further in the ACPI case. It's
>> useful for other stuff but it might well be a distraction and
>> implementation detail in terms of the basic question about what is needed
>> for something like Android.
>>
>> At this point the input of the Android team and the Nokia people would
>> be rather more useful to me.
>
> OK, I added Arve and Brian to the CC list.
>

Even if we used the proposed QoS replacement, are there suggestions on
how to keep the cpu idle for longer than 2 seconds in Linux without
using suspend?

On a thread somewhere I had real world power numbers on a Motorola
Droid idling (screen off) with and without suspend blockers.

-- Mike

> Thanks,
> Rafael
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