linux-kernel - Re: [RFC] PM / devfreq: Add support for alerts

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Message-ID: <f099a5b1-bd4e-d888-92c1-7366820881e8@codeaurora.org>
Date:   Fri, 1 Jun 2018 17:13:47 +0530
From:   Akhil P Oommen <akhilpo@...eaurora.org>
To:     myungjoo.ham@...sung.com,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mka@...omium.org" <mka@...omium.org>
Cc:     "jcrouse@...eaurora.org" <jcrouse@...eaurora.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [RFC] PM / devfreq: Add support for alerts



On 5/31/2018 11:47 AM, MyungJoo Ham wrote:
>> Currently, DEVFREQ reevaluates the device state periodically and/or
>> based on the OPP list changes. Private API has to be exposed to allow
>> the device driver to alert/notify the governor to reevaluate when a new
>> set of data is available. This makes the governor more coupled to a
>> particular device driver. We can improve here by exposing a DEVFREQ API
>> to allow the device drivers to send generic alerts to the governor.
>>
>> Signed-off-by: Akhil P Oommen <akhilpo@...eaurora.org>
>> ---
>>   drivers/devfreq/devfreq.c  | 21 +++++++++++++++++++++
>>   drivers/devfreq/governor.h |  1 +
>>   include/linux/devfreq.h    |  5 +++++
>>   3 files changed, 27 insertions(+)
>>
> Hello Akhil,
>
> It appears that this will have the same effect with
> "[PATCH 08/11] PM / devfreq: Make update_devfreq() public" from Matthias Kaehlcke, doesn't it?
>
>
> Cheers,
> MyungJoo
>
Hi MyngJoo,

The patch you mentioned is a step in the right direction. But this patch 
allows:
1. the governor to decide whether to reevaluate or not. I feel it would 
be a better architecture (better Separation of Concern) if that decision 
is left to the governor alone.
2. the devices to share multiple types of alerts. A governor may use 
these alerts for internal bookkeeping/algorithm and decide to reevaluate 
policy when it is necessary. Since we are opening up a new devfreq API 
for devices, isn't it better to go for a generic one?

Regards,
Akhil.