linux-kernel - Re: suspend blockers & Android integration

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Date:	Sat, 5 Jun 2010 18:45:58 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, tytso@....edu,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	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

2010/6/5 Thomas Gleixner <tglx@...utronix.de>:
> On Sat, 5 Jun 2010, Arve Hjønnevåg wrote:
>> 2010/6/5 Thomas Gleixner <tglx@...utronix.de>:
>> > On Sat, 5 Jun 2010, Arve Hjønnevåg wrote:
>> >> 2010/6/5 Thomas Gleixner <tglx@...utronix.de>:
>> >> > B1;2005;0cOn Fri, 4 Jun 2010, Arve Hjønnevåg wrote:
>> >> Cross app calls do not go through a central process.
>> >
>> > It's not about a central process, it goes through your framework,
>> > which should be able to deal with it. If not, it's a design failure
>> > which needs to be fixed at the place where the failure happened.
>> >
>> >> >>
>> >> >> How can it be fixed? The user presses the back button, the framework
>> >> >> determines that app A is in the foreground and send the key to app A,
>> >> >> app A decides that it it does not have anything internal to go back to
>> >> >> and tells the framework to switch back to the previous app. If the
>> >> >> user presses the back key again, the framework does not know which app
>> >> >> this key should go to until app A has finished processing the first
>> >> >> key press.
>> >> >
>> >> > Errm, what has this to do with frozen apps? If your system is
>> >> > handling input events then there are no frozen apps and even if they
>> >> > are frozen your framework can unfreeze them _before_ talking to them.
>> >> >
>> >> > So which unfixable problem are you describing with the above example ?
>> >> >
>> >>
>> >> You are claiming that trusted code should not have any dependencies on
>> >> untrusted code. I gave you a visible example of such a dependency and
>> >> want you to tell me how you can avoid this dependency. Since you are
>> >> claiming that our user-space framework is fundamentally broken if it
>> >> has to wait for untrusted code, I don't think it is unreasonable for
>> >> you to answer this. Or do you think it is valid to communicate with
>> >> untrusted code when the screen is on but not when it is off.
>> >
>> > It does not matter whether the screen is off or not. If you need to
>> > call into that untrusted app from your trusted app and you know about
>> > the might be frozen state then you can deal with it.
>> >
>> > So taking your example:
>> >
>> > Event happens and gets delivered to the framework
>> >
>> >      framework selects A because it is in the foreground
>> >
>> >      if (A is frozen)
>> >         unfreeze(A)
>> >
>> >      deliver_event_to(A)
>> >
>> > It's that simple.
>> >
>>
>> That is too simple. You also have to prevent A from being frozen while
>> it is processing the event or the result would be the same as if it
>> was frozen beforehand.
>
> The framework decides when to freeze the app in the first place (as
> your framework does now when it decides to suspend)
>
>     So it knows whether the app is frozen or not.
>
>     So it knows damend well whether it processed the event or not.
>

Our user-space code is not single-threaded. So just because an app was
not frozen when you checked does not mean it will remain unfrozen. We
can use the same user-space wakelock api we have now to prevent
freezing apps instead of preventing suspend, but we loose any
advantage we get from freezing just a subset of processes this way.

-- 
Arve Hjønnevåg
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