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

[Viresh Kumar]

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.

-- 
viresh