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Date:   Wed, 13 Jun 2018 22:35:03 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "edubezval@...il.com" <edubezval@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "andrea.parri@...rulasolutions.com" 
        <andrea.parri@...rulasolutions.com>,
        "kevin.wangtao@...aro.org" <kevin.wangtao@...aro.org>,
        "leo.yan@...aro.org" <leo.yan@...aro.org>,
        "daniel.thompson@...aro.org" <daniel.thompson@...aro.org>,
        "javi.merino@...nel.org" <javi.merino@...nel.org>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>
Subject: Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection
 framework

On 13/06/2018 22:32, Pandruvada, Srinivas wrote:
> On Wed, 2018-06-13 at 22:19 +0200, Daniel Lezcano wrote:
>> On 13/06/2018 22:07, Pandruvada, Srinivas wrote:
>>> On Wed, 2018-06-13 at 22:00 +0200, Daniel Lezcano wrote:
>>>> On 13/06/2018 17:54, Pandruvada, Srinivas wrote:
>>>>> On Tue, 2018-06-12 at 14:00 +0200, Daniel Lezcano wrote:
>>>>>> Initially, the cpu_cooling device for ARM was changed by
>>>>>> adding a
>>>>>> new
>>>>>> policy inserting idle cycles. The intel_powerclamp driver
>>>>>> does a
>>>>>> similar action.
>>>>>>
>>>>>> Instead of implementing idle injections privately in the
>>>>>> cpu_cooling
>>>>>> device, move the idle injection code in a dedicated framework
>>>>>> and
>>>>>> give
>>>>>> the opportunity to other frameworks to make use of it.
>>>>>>
>>>>>> The framework relies on the smpboot kthreads which handles
>>>>>> via
>>>>>> its
>>>>>> main loop the common code for hotplugging and [un]parking.
>>>>>>
>>>>>> This code was previously tested with the cpu cooling device
>>>>>> and
>>>>>> went
>>>>>> through several iterations. It results now in split code and
>>>>>> API
>>>>>> exported in the header file. It was tested with the cpu
>>>>>> cooling
>>>>>> device
>>>>>> with success.
>>>>>>
>>>>>
>>>>> May be I have missed, but I don't see any use of powercap
>>>>> sysfs.
>>>>>
>>>>> We created powercap sys that user space is presented a common
>>>>> interface
>>>>> for power capping. The RAPL driver was also submitted as
>>>>> cooling
>>>>> device
>>>>> before, but suggestion was to create this powercap.
>>>>>
>>>>> So if powercap interface is not enough then may be we should
>>>>> enhance
>>>>> that.
>>>>
>>>> We are creating a framework for idle injection. This framework
>>>> can
>>>> then
>>>> be used by the cpu_cooling device, the power_clamp and in
>>>> addition a
>>>> power capping for ARM (if it makes sense).
>>>
>>> But in this case, why in drivers/powercap folder as this is another
>>> framework?
>>
>> I presented at OSPM 2nd the cpu idle cooling device. It is ARM
>> specific
>> but has some similarities with the power clamp driver.
>>
>> Some board come with power numbers defined in their DT and from there
>> we
>> are able to compute a targeted power by injecting idle cycles.
>>
>> As the idle injection allows to do also power capping, Rafael told me
>> to
>> move that to a framework (may be better say a component with exported
>> services or library) and put it in drivers/powercap.
> So Rafael wants it to be in powercap.

That is what I understood.




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