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

[Daniel Lezcano]

On 07/06/2018 10:42, Viresh Kumar wrote:
> On 07-06-18, 10:32, Peter Zijlstra wrote:
>> On Thu, Jun 07, 2018 at 10:18:27AM +0200, Daniel Lezcano wrote:
>>> So IIUC, neither atomic or WRITE|READ_ONCE are necessary in this code
>>> because of the wake_up_process() barrier is enough, right ?
>>
>> I didn't look hard enough; if there ever is a time where the loads and
>> stores happen concurrently, you need READ/WRITE_ONCE(). If there is no
>> concurrency on the variables, you don't need anything.
>>
>> Neither atomic_read/set() nor REAd/WRITE_ONCE() will help with ordering,
>> which is what the wake_up_process() would provide here, different things
>> entirely.
> 
> Right and you still need the READ/WRITE_ONCE() thing as
> idle_injection_set_duration() may run in parallel with the idle_injection_fn()
> thread.
> 
> And I don't think the purpose of atomic_read/write was ever to take care of the
> ordering issues in this code, it was always about parallel loads/stores.

Yes, correct.

But if we don't care about who wins to store to value, is there a risk
of scramble variable if we just assign a value ?


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