linux-kernel - Re: [PATCH v3] cpufreq: powernv: Set the cpus to nominal frequency during reboot/kexec

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Message-ID: <4913652.kENFQcqa9E@vostro.rjw.lan>
Date:	Fri, 26 Sep 2014 01:52:09 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH v3] cpufreq: powernv: Set the cpus to nominal frequency during reboot/kexec

On Thursday, September 11, 2014 05:03:22 PM Viresh Kumar wrote:
> On 11 September 2014 15:43, Shilpasri G Bhat
> <shilpa.bhat@...ux.vnet.ibm.com> wrote:
> > This patch ensures the cpus to kexec/reboot at nominal frequency.
> > Nominal frequency is the highest cpu frequency on PowerPC at
> > which the cores can run without getting throttled.
> >
> > If the host kernel had set the cpus to a low pstate and then it
> > kexecs/reboots to a cpufreq disabled kernel it would cause the target
> > kernel to perform poorly. It will also increase the boot up time of
> > the target kernel. So set the cpus to high pstate, in this case to
> > nominal frequency before rebooting to avoid such scenarios.
> >
> > The reboot notifier will set the cpus to nominal frequncy.
> >
> > Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
> > Suggested-by: Viresh Kumar <viresh.kumar@...aro.org>
> > Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> > ---
> > Changes v2->v3:
> > We return EBUSY when cpufreq governor tries to change the frequency
> > after rebooting is set to true. This results in console being flushed
> > with error messages indicating failed attempts to change the
> > frequency. So instead of returning EBUSY we return 0 to stop the
> > governor from changing the frequency without alerting a failure to
> > do the same on reboot, as this  is not an errorneaos condition.
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Queued up for 3.18, thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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