linux-kernel - Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver

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Date:   Wed, 4 Apr 2018 10:50:02 +0200
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, javi.merino@...nel.org,
        rui.zhang@...el.com, daniel.thompson@...aro.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu
 idle cooling driver

On 26/02/2018 05:30, Viresh Kumar wrote:

[ ... ]

>>>> +
>>>> +	for_each_possible_cpu(cpu) {
>>>> +		cpumask = topology_core_cpumask(cpu);
>>>> +
>>>> +		cct = per_cpu_ptr(&cpuidle_cooling_tsk, cpu);
>>>> +
>>>> +		/*
>>>> +		 * This condition makes the first cpu belonging to the
>>>> +		 * cluster to create a cooling device and allocates
>>>> +		 * the structure. Others CPUs belonging to the same
>>>> +		 * cluster will just increment the refcount on the
>>>> +		 * cooling device structure and initialize it.
>>>> +		 */
>>>> +		if (cpu == cpumask_first(cpumask)) {
>>>
>>> Your function still have few assumptions of cpu numbering and it will
>>> break in few cases. What if the CPUs on a big Little system (4x4) are
>>> present in this order: B L L L L B B B  ??
>>>
>>> This configuration can happen if CPUs in DT are marked as: 0-3 LITTLE,
>>> 4-7 big and a big CPU is used by the boot loader to bring up Linux.
>>
>> Ok, how can I sort it out ?
> 
> I would do something like this:
> 
>         cpumask_copy(possible, cpu_possible_mask);
>         
>         while (!cpumask_empty(possible)) {
>                 first = cpumask_first(possible);
>                 cpumask = topology_core_cpumask(first);
>                 cpumask_andnot(possible, possible, cpumask);
>         
>                 allocate_cooling_dev(first); //This is most of this function in your patch.
>         
>                 while (!cpumask_empty(cpumask)) {
>                         temp = cpumask_first(possible);
>                         //rest init "temp"
>                         cpumask_clear_cpu(temp, cpumask);
>                 }
>         
>                 //Everything done, register cooling device for cpumask.
>         }


Mmh, that sounds very complex. May be it is simpler to count the number
of cluster and initialize the idle_cdev for each cluster and then go for
this loop with the cluster cpumask.




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