linux-kernel - Re: [PATCH 0/3] cpuidle: updates related to tick_broadcast

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Message-ID: <3891627.8vhHP2jkbR@vostro.rjw.lan>
Date:	Tue, 12 May 2015 01:14:01 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"rlippert@...gle.com" <rlippert@...gle.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 0/3] cpuidle: updates related to tick_broadcast_enter() failures

On Monday, May 11, 2015 04:13:37 PM Sudeep Holla wrote:
> 
> On 10/05/15 00:15, Rafael J. Wysocki wrote:
> > On Saturday, May 09, 2015 10:33:05 PM Rafael J. Wysocki wrote:
> >> On Saturday, May 09, 2015 10:11:41 PM Rafael J. Wysocki wrote:
> >>> On Saturday, May 09, 2015 11:19:16 AM Preeti U Murthy wrote:
> >>>> Hi Rafael,
> >>>>
> >>>> On 05/08/2015 07:48 PM, Rafael J. Wysocki wrote:
> >>>
> >>> [cut]
> >>>
> >>>>>>
> >>>>>> +	/* Take note of the planned idle state. */
> >>>>>> +	idle_set_state(smp_processor_id(), target_state);
> >>>>>
> >>>>> And I wouldn't do this either.
> >>>>>
> >>>>> The behavior here is pretty much as though the driver demoted the state chosen
> >>>>> by the governor and we don't call idle_set_state() again in those cases.
> >>>>
> >>>> Why is this wrong?
> >>>
> >>> It is not "wrong", but incomplete, because demotions done by the cpuidle driver
> >>> should also be taken into account in the same way.
> >>>
> >>> But I'm seeing that the recent patch of mine that made cpuidle_enter_state()
> >>> call default_idle_call() was a mistake, because it might confuse find_idlest_cpu()
> >>> significantly as to what state the CPU is in.  I'll drop that one for now.
> >>
> >> OK, done.
> >>
> >> So after I've dropped it I think we need to do three things:
> >> (1) Move the idle_set_state() calls to cpuidle_enter_state().
> >> (2) Make cpuidle_enter_state() call default_idle_call() again, but this time
> >>      do that *before* it has called idle_set_state() for target_state.
> >> (3) Introduce demotion as per my last patch.
> >>
> >> Let me cut patches for that.
> >
> > Done as per the above and the patches follow in replies to this messge.
> >
> > All on top of the current linux-next branch of the linux-pm.git tree.
> >
> 
> Tested on ARM Vexpress platforms with one of the CPU in broadcast mode
> and also with broadcast timer. So, you can add:
> 
> Tested-by: Sudeep Holla <sudeep.holla@....com>

Thanks!

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