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

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Date:   Mon, 30 Jul 2018 11:58:36 -0700
From:   skannan@...eaurora.org
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        rjwysocki@...il.com
Subject: Re: [PATCH] PM / devfreq: Generic cpufreq governor

On 2018-07-29 03:52, Rafael J. Wysocki wrote:
> On Sat, Jul 28, 2018 at 5:56 AM, Saravana Kannan 
> <skannan@...eaurora.org> wrote:
>> 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 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.
>> 
>> To decide the frequency of the device, the governor does one of the
>> following:
>> 
>> * Uses a CPU frequency to device frequency mapping table
>>   - Either one mapping table used for all CPU freq policies (typically 
>> used
>>     for system with homogeneous cores/clusters that have the same 
>> OPPs.
>>   - One mapping table per CPU freq policy (typically used for ASMP 
>> systems
>>     with heterogeneous CPUs with different OPPs)
>> 
>> OR
>> 
>> * Scales the device frequency in proportion to the CPU frequency. So, 
>> if
>>   the CPUs are running at their max frequency, the device runs at its 
>> max
>>   frequency.  If the CPUs are running at their min frequency, the 
>> device
>>   runs at its min frequency. And interpolated for frequencies in 
>> between.
> 
> While not having looked at the details of the patch yet, I would
> change the name of the feature to "Generic cpufreq transition
> governor" to make it somewhat less ambiguous.

In my opinion it makes it look MORE like this is a cpufreq governor. How 
about the following?
PM / devfreq: Generic cpufreq to devfreq mapping governor
Seem a lot more clear to me.

I'm open to suggestions for the devfreq governor name too. "cpufreq" has 
been very confusing so far.
cpufreq-map maybe?

Thanks,
Saravana