linux-kernel - Re: [PATCH 5/8] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver

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Date:   Fri, 16 Feb 2018 18:39:35 +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>
Subject: Re: [PATCH 5/8] thermal/drivers/cpu_cooling: Introduce the cpu idle
 cooling driver


Hi Viresh,

sorry for the late reply.


On 09/02/2018 10:41, Viresh Kumar wrote:
> On 07-02-18, 11:34, Daniel Lezcano wrote:
>> On 07/02/2018 10:12, Viresh Kumar wrote:
>>> What about cpuidle_cooling_unregister() ?
>>
>> The unregister function is not needed because cpuidle can't be unloaded.
>> The cpuidle cooling device is registered after the cpuidle successfully
>> initialized itself, there is no error path.
> 
> Okay, then there are two more things here.
> 
> First, you don't need a kref in your patch and simple counter should
> be used instead, as kref is obviously more heavy to be used for the
> single error path here.

I prefer to keep the kref for its API.

And I disagree about the heavy aspect :)

struct kref {
        refcount_t refcount;
};


> Secondly, what about CPU hotplug ? For example, the cpu-freq cooling
> device gets removed currently if all CPUs of a cluster are
> hotplugged-out. But with your code, even if the CPUs are gone, their
> cpu-idle cooling device will stay.

Yes and it will continue to compute the state, so if new CPUs are
inserted the cooling device automatically uses the cooling state.
I don't see a problem with that.

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