linux-kernel - Re: [PATCH 1/7] cpufreq: remove redundant CPUFREQ

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Date:	Wed, 06 Apr 2016 14:29:21 -0700
From:	Saravana Kannan <skannan@...eaurora.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
CC:	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Fabian Frederick <fabf@...net.be>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Jonathan Corbet <corbet@....net>, Len Brown <lenb@...nel.org>,
	open@...eaurora.org,
	"list@...eaurora.org:ACPI" <linux-acpi@...r.kernel.org>,
	open@...eaurora.org,
	"list@...eaurora.org:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open@...eaurora.org,
	"list@...eaurora.org:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	Nicholas Mc Guire <hofrat@...dl.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 1/7] cpufreq: remove redundant CPUFREQ_INCOMPATIBLE notifier
 event

On 04/06/2016 02:21 PM, Rafael J. Wysocki wrote:
> On Wed, Apr 6, 2016 at 10:30 PM, Saravana Kannan <skannan@...eaurora.org> wrote:
>> On 09/09/2015 05:53 PM, Rafael J. Wysocki wrote:
>>>
>>> Hi,
>>>
>>> On Thu, Sep 10, 2015 at 2:39 AM, Viresh Kumar <viresh.kumar@...aro.org>
>>> wrote:
>>>>
>>>> On 10-09-15, 01:26, Rafael J. Wysocki wrote:
>>>>>
>>>>> On Monday, August 03, 2015 08:36:14 AM Viresh Kumar wrote:
>>>>>>
>>>>>> What's being done from CPUFREQ_INCOMPATIBLE, can also be done with
>>>>>> CPUFREQ_ADJUST. There is nothing special with CPUFREQ_INCOMPATIBLE
>>>>>> notifier.
>>>>>
>>>>>
>>>>> The above part of the changelog is a disaster to me. :-(
>>>>>
>>>>> It not only doesn't explain what really goes on, but it's actively
>>>>> confusing.
>>>>>
>>>>> What really happens is that the core sends CPUFREQ_INCOMPATIBLE
>>>>> notifications
>>>>> unconditionally right after sending the CPUFREQ_ADJUST ones, so the
>>>>> former is
>>>>> just redundant and it's more efficient to merge the two into one.
>>>>
>>>>
>>>> Undoubtedly this looks far better :)
>>>>
>>>> But, isn't this series already applied some time back ?
>>>
>>>
>>> Right, never mind.  For some reason that patch was left in the "New"
>>> state.
>>>
>>> The code is OK.
>>
>>
>>
>> I guess I didn't notice this change when it was sent out.
>>
>> The comment that was deleted in this patch clearly states why the
>> INCOMPATIBLE notifier is needed. Some client might want to boost the CPU min
>> freq for performance or other reasons, but thermal might want to limit it.
>> So, by having thermal register for INCOMPATIBLE notifiers to enforce the
>> limits, we provide a way to guarantee it gets the final say.
>>
>> The real fix should have been to change drivers/thermal/cpu_cooling.c to use
>> CPUFREQ_INCOMPATIBLE instead of CPUFREQ_ADJUST.
>>
>> Is there something I'm missing? If not, can we please revert this patch?
>
> Well, nobody was using that event.
>

True, but that's more of a bug in drivers/thermal/cpu-cooling.c and 
drivers/acpi/processor_thermal.c. We should revert this patch and fix 
those drivers. Does that seem acceptable to you?

-Saravana


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