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

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Date:	Sun, 30 May 2010 22:02:39 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Florian Mickler <florian@...kler.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul@...p1.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>, felipe.balbi@...ia.com,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Saturday 29 May 2010, Arve Hjønnevåg wrote:
> 2010/5/29 Rafael J. Wysocki <rjw@...k.pl>:
> > On Saturday 29 May 2010, Arve Hjønnevåg wrote:
> >> 2010/5/28 Rafael J. Wysocki <rjw@...k.pl>:
> >> > On Friday 28 May 2010, Arve Hjønnevåg wrote:
> >> >> On Fri, May 28, 2010 at 1:44 AM, Florian Mickler <florian@...kler.org> wrote:
> >> >> > On Thu, 27 May 2010 20:05:39 +0200 (CEST)
> >> >> > Thomas Gleixner <tglx@...utronix.de> wrote:
> >> > ...
> >> >> > To integrate this with the current way of doing things, i gathered it
> >> >> > needs to be implemented as an idle-state that does the suspend()-call?
> >> >> >
> >> >>
> >> >> I think it is better no not confuse this with idle. Since initiating
> >> >> suspend will cause the system to become not-idle, I don't think is is
> >> >> beneficial to initiate suspend from idle.
> >> >
> >> > It is, if the following two conditions hold simultaneously:
> >> >
> >> > (a) Doing full system suspend is ultimately going to bring you more energy
> >> >    savings than the (presumably lowest) idle state you're currently in.
> >> >
> >> > (b) You anticipate that the system will stay idle for a considerably long time
> >> >    such that it's worth suspending.
> >> >
> >>
> >> I still don't think this matters. If you are waiting for in interrupt
> >> that cannot wake you up from suspend, then idle is not an indicator
> >> that it is safe to enter suspend. I also don't think you can avoid any
> >> user-space suspend blockers by delaying suspend until the system goes
> >> idle since any page fault could cause it to go idle. Therefore I don't
> >> see a benefit in delaying suspend until idle when the last suspend
> >> blocker is released (it would only mask possible race conditions).
> >
> > I wasn't referring to suspend blockers, but to the idea of initiating full
> > system suspend from idle, which I still think makes sense.  If you are
> > waiting for an interrupt that cannot wake you from suspend, then
> > _obviously_ suspend should not be started.  However, if you're not waiting for
> > such an interrupt and the (a) and (b) above hold, it makes sense to start
> > suspend from idle.
> >
> 
> What about timers? When you suspend timers stop (otherwise it is just
> a deep-idle mode), and this could cause problems. Some drivers rely on
> timers if the hardware does not have a completion interrupt. It is not
> uncommon to see send command x then wait 200ms in a some hardware
> specs.

QoS should be used in such cases.

Rafael
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