linux-kernel - Re: [linux-pm] suspend blockers & Android integration

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Date:	Sun, 6 Jun 2010 16:29:46 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Vitaly Wool <vitalywool@...il.com>
Cc:	Brian Swetland <swetland@...gle.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Arjan van de Ven <arjan@...radead.org>, tytso@....edu,
	Florian Mickler <florian@...kler.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, Neil Brown <neilb@...e.de>,
	James Bottomley <James.Bottomley@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Felipe Balbi <felipe.balbi@...ia.com>
Subject: Re: [linux-pm] suspend blockers & Android integration

On Sun, Jun 06, 2010 at 05:26:09PM +0200, Vitaly Wool wrote:
> 2010/6/6 Matthew Garrett <mjg59@...f.ucam.org>:
> > Holding a suspend blocker is entirely orthogonal to runtime pm. The
> > "whole kernel" will not be "active" - it can continue to hit the same
> > low power state in the idle loop, and any runtime pm implementation in
> > the drivers will continue to be active.
> 
> Yeah, that might also be the case, But then again, what's the use of
> suspend blockers in this situation?

The difference between idle-based suspend and opportunistic suspend is 
that the former will continue to wake up for timers and will never be 
entered if something is using CPU, whereas the latter will be entered 
whenever no suspend blocks are held. The problem with opportunistic 
suspend is that you might make the decision to suspend simultaneusly 
with a wakeup event being received. Suspend blocks facilitate 
synchronisation between the kernel and userspace to ensure that all such 
events have been consumed and handld appropriately.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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