linux-kernel - Re: [PATCH 8/8] thermal/drivers/cpu_cooling: Add the combo cpu cooling device

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Message-ID: <54081703-c48f-3e07-b79d-3a2831bc28d7@linaro.org>
Date:   Tue, 6 Feb 2018 11:48:59 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     edubezval@...il.com, kevin.wangtao@...aro.org, leo.yan@...aro.org,
        vincent.guittot@...aro.org, amit.kachhap@...il.com,
        linux-kernel@...r.kernel.org, Zhang Rui <rui.zhang@...el.com>,
        Javi Merino <javi.merino@...nel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        daniel.thompson@...aro.org
Subject: Re: [PATCH 8/8] thermal/drivers/cpu_cooling: Add the combo cpu
 cooling device

On 06/02/2018 05:28, Viresh Kumar wrote:
> On 05-02-18, 11:32, Daniel Lezcano wrote:
>> On 05/02/2018 05:17, Viresh Kumar wrote:
>>> Right, but I thought the cooling-maps can help us specify different cooling
>>> states for different cooling devices for the same trip point. Maybe my
>>> understanding of that is incorrect.
> 
> Any inputs on this? I am still wondering if this can be done.

Can you give an example? Or your understanding is incorrect or I missed
the point.

>> At the first glance, it sounds interesting but I'm afraid that raises
>> more corner-cases than it solves because we have to take into account
>> all the combinations: cpuidle=0 && cpufreq=1, cpuidle=1 && cpufreq=0,
>> cpuidle=1 && cpufreq=1 with dynamic code changes when the cpufreq driver
>> is loaded/unloaded.
>>
>> I'm not against this approach as well as merging all the cpu cooling
>> devices into a single one but that won't be trivial and will need
>> several iterations before reaching this level of features.
>>
>> IMO, we should keep the current approach (but handle the cpufreq
>> loading/unloading) and then iteratively merge all the cooling device
>> into a single one with policy change at runtime which will automatically
>> handle the cpufreq load/unload.
> 
> Surely we can do one thing at a time if that's the way we choose to do it.

Easy to say :)

The current code is to introduce the feature without impacting the DT
bindings in order to keep focused on the thermal mitigation aspect.

There are still a lot of improvements to do after that. You are
basically asking me to implement the copy-on-write before the memory
management is complete.





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