linux-kernel - Re: [PATCH v3 0/2] Add stop callback to the cpufreq

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Message-ID: <53289D9A.8070805@gmail.com>
Date:	Tue, 18 Mar 2014 12:25:14 -0700
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	dirk.brandewie@...il.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, rjw@...ysocki.net,
	patrick.marlier@...il.com, viresh.kumar@...aro.org,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH v3 0/2] Add stop callback to the cpufreq_driver interface.

On 03/18/2014 12:08 PM, Srivatsa S. Bhat wrote:
> On 03/18/2014 10:52 PM, dirk.brandewie@...il.com wrote:
>> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
>>
>
> I don't mean to nitpick, but generally its easier to deal with
> patchsets if you post the subsequent versions in fresh email threads.
> Otherwise it can get a bit muddled along with too many other email
> discussions in the same thread :-(
>
>> Changes:
>> v2->v3
>> Changed the calling of the ->stop() callback to be conditional on the
>> core being the last core controlled by a given policy.
>>
>
> Wait, why? I'm sorry if I am not catching up with the discussions on
> this issue quickly enough, but I don't see why we should make it
> conditional on _that_. I thought we agreed that we should make it
> conditional in the sense that ->stop() should be invoked only for
> ->setpolicy drivers, right?

This was done at Viresh's suggestion since thought there might be value
for ->target drivers.

Any of the options work for me
    called only for set_policy scaling drivers
    called unconditionally for all scaling drivers
    called for last core controlled by a given policy

>
> The way I look at it, ->stop() gives you a chance to stop managing
> the CPU going offline. As in "stop this CPU". ->exit() is your chance
> to cleanup the policy, since all its users have gone offline (or this
> is the last CPU belonging to that policy which is going offline).
>
> With this in mind, we should invoke ->stop() every time we take a
> CPU offline, and invoke ->exit() only when the last CPU in the policy
> goes offline.

This is exactly what will happen for intel_pstate since the policies cover
a single core.

I will defer to you and Viresh how policies that affect more that one
cpu should be handled.

What intel_pstate needs it to be called during the PREPARE phase of the
offline process.

>
> What am I missing?
>
> Regards,
> Srivatsa S. Bhat
>

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