linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

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Date:	Fri, 14 May 2010 09:06:50 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Paul Walmsley <paul@...an.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	magnus.damm@...il.com, Theodore Ts'o <tytso@....edu>,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>,
	Brian Swetland <swetland@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Benoît Cousson <b-cousson@...com>,
	linux-omap@...r.kernel.org, Vitaly Wool <vitalywool@...il.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

Matthew Garrett <mjg@...hat.com> writes:

> On Thu, May 13, 2010 at 01:00:04PM -0700, Tony Lindgren wrote:
>
>> The system stays running because there's something to do. The system
>> won't suspend until all the processors hit the kernel idle loop and
>> the next_timer_interrupt_critical() returns nothing.
>
> At which point an application in a busy loop cripples you. I think we 
> could implement your suggestion more easily by just giving untrusted 
> applications an effectively infinite amount of timer slack, 
>
> but it still doesn't handle the case where an app behaves
> excrutiatingly badly.

Is design for exruciatingly bad apps a design requirement?

If so, opportunistic suspend + suspend blockers fails as well.  An app
could easily hold a suspend blocker during its entire execution
crippling PM.

Using opportunistic suspend may possibly allow you contain bad
apps/drivers, but at the cost of having to patch already working and
trusted apps and known-working kernel code with suspend blockers.

IMO, rather than accepting a solution that allows bad apps to run
wild, it would be much better to _continue_ focus on tools for finding
and containing bad apps.  This approach has the added bonus of solving
problems on *every* linux-based system, not just Android.

Kevin
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