linux-kernel - Re: [PATCH] tick/idle/powerpc: Do not register idle states with CPUIDLE_FLAG_TIMER

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Message-ID: <CAJZ5v0iR_gOXahW5WtgecaTnb6g6RRMaa=4kOiHR2tBghfo++A@mail.gmail.com>
Date:	Thu, 25 Jun 2015 00:28:23 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Michael Ellerman <michael@...erman.id.au>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	mpe@...erman.id.au, Will Deacon <will.deacon@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	shreyas@...ux.vnet.ibm.com, svaidy@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] tick/idle/powerpc: Do not register idle states with
 CPUIDLE_FLAG_TIMER_STOP set in periodic mode

On Thu, Jun 25, 2015 at 12:10 AM, Michael Ellerman
<michael@...erman.id.au> wrote:
>
>
> On 24 June 2015 23:50:40 GMT+10:00, "Rafael J. Wysocki" <rjw@...ysocki.net> wrote:
>>On Wednesday, June 24, 2015 01:48:01 AM Preeti U Murthy wrote:
>>> On some archs, the local clockevent device stops in deep cpuidle
>>states.
>>> The broadcast framework is used to wakeup cpus in these idle states,
>>in
>>> which either an external clockevent device is used to send wakeup
>>ipis
>>> or the hrtimer broadcast framework kicks in in the absence of such a
>>> device. One cpu is nominated as the broadcast cpu and this cpu sends
>>> wakeup ipis to sleeping cpus at the appropriate time. This is the
>>> implementation in the oneshot mode of broadcast.
>>>
>>> In periodic mode of broadcast however, the presence of such cpuidle
>>> states results in the cpuidle driver calling tick_broadcast_enable()
>>> which shuts down the local clockevent devices of all the cpus and
>>> appoints the tick broadcast device as the clockevent device for each
>>of
>>> them. This works on those archs where the tick broadcast device is a
>>> real clockevent device.  But on archs which depend on the hrtimer
>>mode
>>> of broadcast, the tick broadcast device hapens to be a pseudo device.
>>> The consequence is that the local clockevent devices of all cpus are
>>> shutdown and the kernel hangs at boot time in periodic mode.
>>>
>>> Let us thus not register the cpuidle states which have
>>> CPUIDLE_FLAG_TIMER_STOP flag set, on archs which depend on the
>>hrtimer
>>> mode of broadcast in periodic mode. This patch takes care of doing
>>this
>>> on powerpc. The cpus would not have entered into such deep cpuidle
>>> states in periodic mode on powerpc anyway. So there is no loss here.
>>>
>>> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
>>
>>4.2 material I suppose?
>
> Yes please, in fact it should be marked for stable too.

That can be done.  Which -stable series should it go into?

Rafael
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