Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle injection framework

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 06/06/2018 17:02, Peter Zijlstra wrote:
> On Wed, Jun 06, 2018 at 03:42:08PM +0200, Daniel Lezcano wrote:
>> On 06/06/2018 14:23, Peter Zijlstra wrote:
>>> On Tue, Jun 05, 2018 at 11:16:40AM +0200, Daniel Lezcano wrote:
>>>> +	atomic_t idle_duration_ms;
>>>> +	atomic_t run_duration_ms;
>>>
>>>> +	idle_duration_ms = atomic_read(&ii_dev->idle_duration_ms);
>>>
>>>> +	run_duration_ms = atomic_read(&ii_dev->run_duration_ms);
>>>
>>>> +	atomic_set(&ii_dev->run_duration_ms, run_duration_ms);
>>>> +	atomic_set(&ii_dev->idle_duration_ms, idle_duration_ms);
>>>
>>>> +	*run_duration_ms = atomic_read(&ii_dev->run_duration_ms);
>>>> +	*idle_duration_ms = atomic_read(&ii_dev->idle_duration_ms);
>>>
>>>> +	if (!atomic_read(&ii_dev->idle_duration_ms))
>>>
>>>> +	if (!atomic_read(&ii_dev->run_duration_ms))
>>>
>>> What is the point of atomic_t here ?!
>>
>> idle_duration and run_duration can be changed from different places at
>> the same time. The atomic is here to ensure the read/write are consistent.
>>
>> Do you think it is pointless ?
> 
> Yes, atomic_read() / atomic_set() are no more atomic than READ_ONCE() /
> WRITE_ONCE().

So IIUC, neither atomic or WRITE|READ_ONCE are necessary in this code
because of the wake_up_process() barrier is enough, right ?


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