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

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Message-ID: <CAKohpo=uB252XLfx3tHPA8uk5RPkWB0SPQ_UxzVw70c-DWuHWg@mail.gmail.com>
Date:	Thu, 11 Sep 2014 17:03:22 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"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 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>
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