linux-kernel - RE: [PATCH 2/2] PM / devfreq: Generic cpufreq governor

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Date:   Mon, 28 May 2018 15:00:14 +0900
From:   MyungJoo Ham <myungjoo.ham@...sung.com>
To:     Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
CC:     Saravana Kannan <skannan@...eaurora.org>,
        Rajendra Nayak <rjendra@...eaurora.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] PM / devfreq: Generic cpufreq governor

>Many CPU architectures have caches that can scale independent of the CPUs.
>Frequency scaling of the caches is necessary to make sure the cache is not
>a performance bottleneck that leads to poor performance and power. The same
>idea applies for RAM/DDR.
>
>To achieve this, this patch series adds a generic devfreq governor that can
>listen to the frequency transitions of each CPU frequency domain and then
>adjusts the frequency of the cache (or any devfreq device) based on the
>frequency of the CPUs.

I agree that we have some hardware pieces that want to configure
frequencies based on the CPUfreq.

Creating a devfreq governor that configures devfreq-freq
based on incoming events (CPUFreq-transition-event in this case)
is indeed a good idea.

However, I would like to ask the followings:
The overall code appears to be overly complex compared what you need.
- Do you really need to revive "CPUFREQ POLICY" events for this?
especially when you are going to look at "first CPU" only?


Cheers,
MyungJoo