linux-kernel - Re: suspend blockers & Android integration

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Date:	Fri, 4 Jun 2010 09:13:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arve Hj?nnev?g <arve@...roid.com>
Cc:	tytso@....edu, Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Kevin Hilman <khilman@...prootsystems.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: suspend blockers & Android integration


* Arve Hj?nnev?g <arve@...roid.com> wrote:

> On Thu, Jun 3, 2010 at 4:23 PM, Ingo Molnar <mingo@...e.hu> wrote:
> ...
> > ?- Controlled auto-suspend: drivers (such as input) could on wakeup
> > ? automatically set the 'minimum wakeup latency' value of wakee tasks to a
> > ? lower value. This automatically prevents another auto-suspend in the near
> > ? future: up to the point the wakee task increases its latency (via the
> > ? scheduler syscall) again and allows suspend again.
> >
> 
> How do you clear the latency value in a safe way? If another wakeup event 
> happens right after your wakee task is done processing the last event and 
> decides to increase its latency, auto suspend will be allowed even though 
> you have an unprocessed wakeup event. Also how do you know which task will 
> read the event if it is not already waiting for it?

The easiest solution would be to not do any of that initially. (If it's ever a 
concern we could subtract/add without destroying the nesting property)

Why do you need to track input wakeups? It's rather fragile and rather 
unnecessary - the idle drivers know it very well how to not go into the 
deepest idle mode already today. We wont hit C8 on laptops when you are using 
the desktop.

> > ? This means there will be no surprise suspends for a task that may take a
> > ? bit longer than usual to finish its work. [ Detail: this would only be done
> > ? for tasks that have a non-default (non-infinity) task->latency value - to
> > ? prevent the input driver from lowering latency values (and preventing
> > ? future suspends) just because some unaware apps are running and using input
> > ? drivers. ]
> 
> Don't you need two inifinity values for this?

Yes - any value above the max idle latency in the system will do.

Thanks,

	Ingo
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