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Date:   Wed, 6 Jun 2018 17:02:03 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Daniel Lezcano <daniel.lezcano@linaro.org>
Cc:     rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Eduardo Valentin <edubezval@gmail.com>,
        Javi Merino <javi.merino@kernel.org>,
        Leo Yan <leo.yan@linaro.org>,
        Kevin Wangtao <kevin.wangtao@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Rui Zhang <rui.zhang@intel.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        "open list:POWER MANAGEMENT CORE" <linux-pm@vger.kernel.org>
Subject: Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle
 injection framework
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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().