linux-kernel - Re: Attempted summary of suspend-blockers LKML thread

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Message-ID: <20100802084003.1c4c2bdb@schatten.dmk.lab>
Date:	Mon, 2 Aug 2010 08:40:03 +0200
From:	Florian Mickler <florian@...kler.org>
To:	david@...g.hm
Cc:	Arjan van de Ven <arjan@...radead.org>, paulmck@...ux.vnet.ibm.com,
	"Ted Ts'o" <tytso@....edu>, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, arve@...roid.com,
	mjg59@...f.ucam.org, pavel@....cz, rjw@...k.pl,
	stern@...land.harvard.edu, swetland@...gle.com,
	peterz@...radead.org, tglx@...utronix.de, alan@...rguk.ukuu.org.uk
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Sun, 1 Aug 2010 23:06:08 -0700 (PDT)
david@...g.hm wrote:

> On Mon, 2 Aug 2010, Florian Mickler wrote:
> 
> > On Sun, 1 Aug 2010 22:06:34 -0700 (PDT)
> > david@...g.hm wrote:
> >
> >> On Sun, 1 Aug 2010, Arjan van de Ven wrote:
> >>
> >>> I'm a little worried that this whole "I need to block suspend" is
> >>> temporary. Yes today there is silicon from ARM and Intel where suspend
> >>> is a heavy operation, yet at the same time it's not all THAT heavy
> >>> anymore.... at least on the Intel side it's good enough to use pretty
> >>> much all the time (when the screen is off for now, but that's a memory
> >>> controller issue more than anything else). I'm pretty sure the ARM guys
> >>> will not be far behind.
> >>
> >> remember that this 'block suspend' is really 'block overriding the fact
> >> that there are still runable processes and suspending anyway"
> >>
> >> having it labeled as 'suspend blocker' or even 'wakelock' makes it sound
> >> as if it blocks any attempt to suspend, and I'm not sure that's what's
> >> really intended. Itsounds like the normal syspend process would continue
> >> to work, just this 'ignore if these other apps are busy' mode of operation
> >> would not work.
> >>
> >> which makes me wonder, would it be possible to tell the normal idle
> >> detection mechanism to ignore specific processes when deciding if it
> >> should suspend or not? how about only considering processes in one cgroup
> >> when deciding to suspend and ignoring all others?
> >>
> >> David Lang
> >
> > We then get again to the "runnable tasks" problem that was
> > discussed earlier... the system get's "deadlock-prone" if a subset of
> > tasks is not run.
> > Interprocess dependencies are not so easy to get right in general.
> 
> I'm not suggesting that you don't run the 'untrusted' tasks, just that you 
> don't consider them when deciding if the system can suspend or not. if the 
> system is awake, everything runs, if the system is idle (except for the 
> activity of the 'untrusted' tasks) you suspend normally.
> 
> David Lang

Ah, yes. Sorry. It's pretty early in the morning over here, I don't
seem to have my eyes fully opened yet... A "ignore-these-processes"
cgroup could probably work... It would have the advantage of not having
to maintain a special purpose API....


Cheers,
Flo




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