linux-kernel - Re: suspend blockers & Android integration

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Date:	Fri, 4 Jun 2010 17:10:48 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, tytso@....edu,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kevin Hilman <khilman@...prootsystems.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: suspend blockers & Android integration

2010/6/4 Peter Zijlstra <peterz@...radead.org>:
> On Fri, 2010-06-04 at 01:56 -0700, Arve Hjønnevåg wrote:
>> On Fri, Jun 4, 2010 at 1:34 AM, Ingo Molnar <mingo@...e.hu> wrote:
>> >
>> > * Arve Hj?nnev?g <arve@...roid.com> wrote:
>> >
>> >> > [...]
>> >> >
>> >> > Why do you need to track input wakeups? It's rather fragile and rather
>> >> > unnecessary [...]
>> >>
>> >> Because we have keys that should always turn the screen on, but the problem
>> >> is not specific to input events. If we enabled a wakeup event it usually
>> >> means we need this event to always work, not just when the system is fully
>> >> awake or fully suspended.
>> >
>> > Hm, i cannot follow that generic claim. Could you please point out the problem
>> > to me via a specific example? Which task does what, what undesirable thing
>> > happens where, etc.
>> >
>>
>> We have many wakeup events, and some of them are invisible to the
>> user. For instance on the Nexus One wake up every 10 minutes monitor
>> the battery health.
>
>> If the user presses a key right after this work
>> has finished and we did not block suspend until userspace could
>> process this key event, we risk suspending before we could turn the
>> screen on, which to the user looks like the key did not work.
>
>> Another
>> example, the user pressed the power key which turns the screen off and
>> allows suspend. We initiate suspend and a phone call comes in. If we
>> don't block suspend until we processed the incoming phone call
>> notification, the phone may never ring (some devices will send a new
>> message every few seconds for this, so on those devices it would just
>> delay the ringing).
>
> Right, so in the proposed scheme all these tasks would be executed by
> trusted processes, and trusted processes will never get frozen and so
> will never be delayed in processing these events.
>

There are many proposes schemes. I assume you mean freezing only
untrusted processes and nothing else.

> Only untrusted code will be frozen. And trusted processes are reliable
> for thawing the untrusted processes and delivering events to it.
>

I have two problems with this. I don't want to funnel all events
trough trusted processes, and I also want to freeze trusted processes.

> Trusted processes are assumed to be sane and idle when there is nothing
> for them to do, allowing the machine to go into deep idle states.
>

Neither the kernel nor our trusted user-space code currently meets
this criteria.

-- 
Arve Hjønnevåg
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