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

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Date:	Sun, 6 Jun 2010 17:47:10 +0200
From:	Vitaly Wool <vitalywool@...il.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
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

2010/6/6 Matthew Garrett <mjg59@...f.ucam.org>:
> 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.

Right, and then you start taking suspend blockers in kernel here and
there which eventually interferes with runtime PM.
So I don't buy the "orthogonality" point. Generally speaking, it's not true.

~Vitaly
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