linux-kernel - Re: suspend blockers & Android integration

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Date:	Fri, 4 Jun 2010 02:39:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	tytso@....edu
Cc:	Brian Swetland <swetland@...gle.com>, Neil Brown <neilb@...e.de>,
	Arve Hj?nnev?g <arve@...roid.com>,
	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


* Ingo Molnar <mingo@...e.hu> wrote:

>  - Create a 'deep idle' mode that suspends. This, if all constraints
>    are met, is triggered by the scheduler automatically: just like the other
>    idle modes are triggered currently. This approach fixes the wakeup
>    races because an incoming wakeup event will set need_resched() and
>    abort the suspend.
> 
>    ( This mode can even use the existing suspend code to bring stuff down,
>      therefore it also solves the pending timer problem and works even on
>      PC style x86. )

Note that this does not necessarily have to be implemented as 'execute suspend 
from the idle task' code: scheduling from the idle task, while can certainly 
be made to work, is a somewhat recursive concept that we might want to avoid 
for robustness reasons.

Instead, the 'deepest idle' (suspend) method could consist of a wakeup of a 
kernel thread (or of any of the existing kernel threads such as the migration 
thread) - which kernel thread then does a race-free suspend: it offlines all 
but one CPU [on platforms that need that] and then initiates the suspend - but 
aborts the attempt if there's any sign of wakeup activity.

Thanks,

	Ingo
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