Re: Attempted summary of suspend-blockers LKML thread, take three

[david]

On Tue, 10 Aug 2010, Matthew Garrett wrote:

> On Tue, Aug 10, 2010 at 09:38:49AM +0100, Alan Cox wrote:
> > > Hmmm...  Exactly which part do you consider flawed?  Let's take it
> > > one sentence at a time.  The devices that I know of that lack suspend
> > > blockers also lack opportunistic suspend.  Therefore, all applications on
> > > such devices run as would an application that acquired a suspend blocker
> > > when it started and did not release that suspend blocker until it exited.
> > > Pretty straightforward.
> >
> > What do you mean by "opportunistic suspend", lots of systems drop into
> > lowest power states whenever they can. "Suspend is different" is a bit of
> > Android religion that I am dubious has any basis in reality as seen from
> > the application end of the universe.
> >
> > You may also wish to review the earlier parts of the discussion where it
> > was explicitly stated by several developers that they were using
> > "suspend" type modes as power states already and not using suspend
> > blockers. So it's being done, today on ARM and your statement is directly
> > contradicting the code. Modern ARM processors and x86 MID devices can
> > suspend and resume extremely fast (fast enough that the fact Linux x86
> > rewriting all the SMP alternatives on suspend/resume is a measurable
> > problem). If this same property doesn't end up on big PC boxes in time
> > then I'd be very surprised. At that point the openoffice with suspend
> > blockers or oracle with suspend blockers question becomes rather relevant.
>
> There's a clear and absolute difference between system suspend and
> entering the same hardware state from the idle loop. That difference is
> that processes aren't scheduled until an explicit wakeup event occurs.
> Android is entirely capable of entering the same low power state at idle
> (it's done with a hardcoded idle loop on Qualcomm, cpuidle on omap), but
> if you have more than 0 scheduling wakeups a second then your power draw
> is going to be greater.
>
> I agree that we should be targetting 0 wakeups per second. I don't agree
> that it's realistic to insist that a use model that assumes imperfect
> software is an invalid use model.

If the primary difference between sleep and suspend is not scheduling 
processes, instead of messing with oppurtinistic suspend/suspend 
blockers/wakelocks/etc, why not just 'temporarily' change the timer fuzz 
value to a very large value (say an hour). That would still let things 
like openoffice saves ahve a fair chance to trigger before the battery 
died completely, but would wake the system so infrequently that it will be 
effectivly the same as a full suspend.

David Lang
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