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SubjectRe: [PATCH 5/8] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver
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On 31/01/2018 10:56, Vincent Guittot wrote:
> On 31 January 2018 at 10:50, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>> On 31/01/2018 10:46, Vincent Guittot wrote:
>>> On 31 January 2018 at 10:33, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>>>> On 31/01/2018 10:01, Vincent Guittot wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> On 23 January 2018 at 16:34, Daniel Lezcano <daniel.lezcano@linaro.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.

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;
};


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