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

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Date:   Thu, 1 Feb 2018 08:57:45 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Eduardo Valentin <edubezval@...il.com>,
        Kevin Wangtao <kevin.wangtao@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        viresh kumar <viresh.kumar@...aro.org>,
        linux-kernel <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

On 31 January 2018 at 16:27, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
> On 31/01/2018 10:56, Vincent Guittot wrote:
>> On 31 January 2018 at 10:50, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>> On 31/01/2018 10:46, Vincent Guittot wrote:
>>>> On 31 January 2018 at 10:33, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>>>> On 31/01/2018 10:01, Vincent Guittot wrote:
>>>>>> Hi Daniel,
>>>>>>
>>>>>> On 23 January 2018 at 16:34, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>>>>
>>>>> [ ... ] (please trim :)
>>>>>
>>>>>>> +               /*
>>>>>>> +                * Each cooling device is per package. Each package
>>>>>>> +                * has a set of cpus where the physical number is
>>>>>>> +                * duplicate in the kernel namespace. We need a way to
>>>>>>> +                * address the waitq[] and tsk[] arrays with index
>>>>>>> +                * which are not Linux cpu numbered.
>>>>>>> +                *
>>>>>>> +                * One solution is to use the
>>>>>>> +                * topology_core_id(cpu). Other solution is to use the
>>>>>>> +                * modulo.
>>>>>>> +                *
>>>>>>> +                * eg. 2 x cluster - 4 cores.
>>>>>>> +                *
>>>>>>> +                * Physical numbering -> Linux numbering -> % nr_cpus
>>>>>>> +                *
>>>>>>> +                * Pkg0 - Cpu0 -> 0 -> 0
>>>>>>> +                * Pkg0 - Cpu1 -> 1 -> 1
>>>>>>> +                * Pkg0 - Cpu2 -> 2 -> 2
>>>>>>> +                * Pkg0 - Cpu3 -> 3 -> 3
>>>>>>> +                *
>>>>>>> +                * Pkg1 - Cpu0 -> 4 -> 0
>>>>>>> +                * Pkg1 - Cpu1 -> 5 -> 1
>>>>>>> +                * Pkg1 - Cpu2 -> 6 -> 2
>>>>>>> +                * Pkg1 - Cpu3 -> 7 -> 3
>>>>>>
>>>>>>
>>>>>> I'm not sure that the assumption above for the CPU numbering is safe.
>>>>>> Can't you use a per cpu structure to point to resources that are per
>>>>>> cpu instead ? so you will not have to rely on CPU ordering
>>>>>
>>>>> Can you elaborate ? I don't get the part with the percpu structure.
>>>>
>>>> Something like:
>>>>
>>>> struct cpuidle_cooling_cpu {
>>>>        struct task_struct *tsk;
>>>>        wait_queue_head_t waitq;
>>>> };
>>>>
>>>> DECLARE_PER_CPU(struct cpuidle_cooling_cpu *, cpu_data);
>>>
>>> I got this part but I don't get how that fixes the ordering thing.
>>
>> Because you don't care of the CPU ordering to retrieve the data as
>> they are stored per cpu directly
>
> That's what I did initially, but for consistency reasons with the
> cpufreq cpu cooling device which is stored in a list and the combo cpu
> cooling device, the cpuidle cooling device must be per cluster and
> stored in a list.

I'm not sure to catch your problem. You can still have cpuidle cooling
device per cluster and stored in the list but keep per cpu data in a

AFAICT, you will not have more than one cpu cooling device registered
per CPU so one per cpu variable that will gathers cpu private data
should be enough ?

>
> Alternatively I can do:
>
> struct cpuidle_cooling_device {
>         struct thermal_cooling_device *cdev;
> -       struct task_struct **tsk;
> +       struct task_struct __percpu *tsk;
>         struct cpumask *cpumask;
>         struct list_head node;
>         struct hrtimer timer;
>         struct kref kref;
> -       wait_queue_head_t *waitq;
> +       wait_queue_head_t __percpu waitq;
>         atomic_t count;
>         unsigned int idle_cycle;
>         unsigned int state;
> };

struct cpuidle_cooling_device {
         struct thermal_cooling_device *cdev;
         struct cpumask *cpumask;
         struct list_head node;
         struct hrtimer timer;
         struct kref kref;
         atomic_t count;
         unsigned int idle_cycle;
         unsigned int state;
};

struct cpuidle_cooling_cpu {
        struct task_struct *tsk;
        wait_queue_head_t waitq;
};
DECLARE_PER_CPU(struct cpuidle_cooling_cpu *, cpu_data);

You continue to have cpuidle_cooling_device allocated dynamically per
cluster and added in the list but task and waitq are stored per cpu

>
>
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