linux-kernel - Re: suspend blockers & Android integration

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Date:	Sat, 5 Jun 2010 15:39:44 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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>
Subject: Re: suspend blockers & Android integration

2010/6/5 Arjan van de Ven <arjan@...radead.org>:
> On Sat, 5 Jun 2010 14:26:14 -0700
> Arve Hjønnevåg <arve@...roid.com> wrote:
>
>> On Sat, Jun 5, 2010 at 9:28 AM, Arjan van de Ven
>> <arjan@...radead.org> wrote:
>> > On Sat, 05 Jun 2010 11:54:13 +0200
>> > Peter Zijlstra <peterz@...radead.org> wrote:
>> >
>> >> On Fri, 2010-06-04 at 17:10 -0700, Arve Hjønnevåg wrote:
>> >> > > 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.
>> >>
>> >> Then both need fixing. Really, that's the only sane approach.
>> >
>> > fwiw... in MeeGo we're seeing quite good idle times (> 1 seconds)
>> > without really bad hacks.
>> >
>>
>> We clearly have different standards for what we consider good. We
>> measure time suspended in minutes or hours, not seconds, and waking up
>> every second or two causes a noticeable decrease in battery life on
>> the hardware we have today.
>
> I guess I'm spoiled working with (unreleased) hardware that knows how
> to power gate ;-)
>
>
>>
>> > the kernel has a set of infrastructure already to help here (range
>> > timers, with which you can wakeup-limit untrusted userspace crap),
>> > timer slack for legacy background timers, etc etc.
>>
>> Range timers allows the kernel to align different timers so they don't
>> each bring the cpu out of idle individually. They do not eliminate
>> timers or make individual timers fire less often.
>
> you're incorrect.
> With range timers you can control the rate at which timers fire just
> fine.
>
> For example if the Adobe Flash player puts a timer every 10
> milliseconds (yes it does that), and you give it a 3.99 seconds range,
> it will fire its timers every 4 seconds.... unless other activity
> happens independently, at which point it'll align with that instead.
>

If you do that what you are delivering is nowhere close to what the
app asked for. You don't need range timers for this, you could just as
well add 4 seconds to all normal timers.

-- 
Arve Hjønnevåg
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