linux-kernel - Re: suspend blockers & Android integration

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Message-ID: <20100603234634.GA21831@elte.hu>
Date:	Fri, 4 Jun 2010 01:46:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	tytso@....edu, 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>,
	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


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, 4 Jun 2010, Ingo Molnar wrote:
> > 
> >    This allows a task to 'exclude' other tasks that dont have low-latency 
> >    requirements. Crappy apps would have a large latency value, so they'd
> >    be idled out when a privileged task sets the exclusion level low enough.
> 
> Quite frankly, this sounds fundamentally broken.
>
> Think deadlock. The high-latency task got a lock, and now you're excluding 
> it because it scheduled away.

Mail was a bit too long already so i trimmed it at the wrong place :-/

What you say is absolutely true, hence this would be driven via sched_tick() + 
TIF notifiers - i.e. only ever treat user-mode tasks as 'idle-able'. This can 
be done with no overhead to the regular fastpaths.

The TIF notifier would be the one scheduling to idle - and would thus do it 
only to user-mode tasks.

Thanks,

	Ingo
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