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

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Message-ID: <20100528000647.GB8645@core.coreip.homeip.net>
Date:	Thu, 27 May 2010 17:06:47 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul@...p1.linux-foundation.org,
	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>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Fri, May 28, 2010 at 12:50:45AM +0100, Alan Cox wrote:
> > That's correct, but to me the Arve's goal is simply to maximize battery life
> > and he found experimentally that the longest battery life is achieved if
> > system suspend is used whenever the system doesn't need to be active (from its
> > user's perspective).  This actually is different from "when the system is
> > idle", because the system isn't idle, for example, when updatedb is running.
> > However, from the user's perspective the updatedb process doesn't really need
> > to run at this particular time, it can very well do it's job in parallel with
> > the user typing or reading news.  So, the system may very well be suspended
> > when updatedb is running.
> 
> This is where the original questions around QoS came in
> 
> > Since I think we've now rejected the feature, do we have a clear picture about
> > what the Android people should do _instead_ and yet keep the battery life they
> > want?  Because I don't think telling "let them do what they want, who cares"
> > is right.
> 
> Today "idle" means "no task running"
> 
> If you are prepared to rephrase that as "no task that matters is running"
> what would need to answer ?
> 
> - How do we define who matters: QoS ?
> 
> - Can you describe "idle" in terms of QoS without then breaking the
>   reliable wakeup for an event (and do you need to ?)
> 
> 	Could this for example look like
> 
> 	Set QoS of 'user apps' to QS_NONE
> 	Button pushed
> 	Button driver sets QoS of app it wakes to QS_ABOVESUSPEND
> 
> 	That would I think solve the reliable wakeup case although
> 	drivers raising a QoS parameter is a bit unusual in the kernel.
> 	That would at least however be specific to a few Android drivers
> 	and maybe a tiny amount of shared driver stuff so probably not
> 	unacceptable. (wake_up_pri(&queue, priority); isn't going to
> 	kill anyone is it - especially if it usually ignores the
> 	priority argument)

That should probably go into higher levels, not in individual drivers,
so we should be able to limit spreading of wake_up_pri() or whatever
throughout the tree.  This particular case should be probably handled by
evdev raising QoS of the user that is opened particular
/dev/input/eventX.

-- 
Dmitry
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