Re: [PATCH 0/8] Suspend block api (version 8)

Rafael J. Wysocki
2010-05-30T20:02:39Z

On Saturday 29 May 2010, Arve Hjønnevåg wrote:
> 2010/5/29 Rafael J. Wysocki <rjw@sisk.pl>:
> > On Saturday 29 May 2010, Arve Hjønnevåg wrote:
> >> 2010/5/28 Rafael J. Wysocki <rjw@sisk.pl>:
> >> > On Friday 28 May 2010, Arve Hjønnevåg wrote:
> >> >> On Fri, May 28, 2010 at 1:44 AM, Florian Mickler <florian@mickler.org> wrote:
> >> >> > On Thu, 27 May 2010 20:05:39 +0200 (CEST)
> >> >> > Thomas Gleixner <tglx@linutronix.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