Re: [PATCH 1/7] cpufreq: remove redundant CPUFREQ_INCOMPATIBLE notifier event

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On 04/06/2016 02:21 PM, Rafael J. Wysocki wrote:
On Wed, Apr 6, 2016 at 10:30 PM, Saravana Kannan <skannan@xxxxxxxxxxxxxx> 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@xxxxxxxxxx>
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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