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

Rafael J. Wysocki
2010-05-28T00:03:55Z

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.

Thanks,
Rafael