linux-kernel - Re: [PATCH 10/16] cpuidle: pseries: Convert to hotplug state machine

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Message-ID: <20160822190404.i56qlimrqkhozacn@linutronix.de>
Date:   Mon, 22 Aug 2016 21:04:04 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, rt@...utronix.de,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 10/16] cpuidle: pseries: Convert to hotplug state machine

On 2016-08-22 18:09:47 [+0200], Daniel Lezcano wrote:
> On 08/18/2016 02:57 PM, Sebastian Andrzej Siewior wrote:
> > Install the callbacks via the state machine.
> > 
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Cc: linux-pm@...r.kernel.org
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > ---
> > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> > index 5811954809af..baecc4faf028 100644
> > --- a/include/linux/cpuhotplug.h
> > +++ b/include/linux/cpuhotplug.h
> > @@ -19,6 +19,7 @@ enum cpuhp_state {
> >  	CPUHP_MM_WRITEBACK_DEAD,
> >  	CPUHP_SOFTIRQ_DEAD,
> >  	CPUHP_NET_MVNETA_DEAD,
> > +	CPUHP_CPUIDLE_PSERIES_DEAD,
> 
> Can't we directly merge these into CPUHP_CPUIDLE_DEAD instead ? Or is it
> planned to be done separately ?

You mean CPUHP_CPUIDLE_DEAD instead of _PSERIES_DEAD and _POWERNV_DEAD?
We could do that but you would have to ensure that only one CPUIDLE
driver registers itself at a time and for those powerpc drivers it looks
like you could have two registered (not sure about ARM's little/big (if
you could have two of those later at run-time)).
For the ONLINE state we have dynamic allocation of IDs. If it is
possible to rework the code to use only ONLINE & PRE_DOWN instead of
DEAD then we wouldn't have this. I can't say at this point if we do
dynamic allocation of the DEAD IDs.

Sebastian