linux-kernel - Re: [PATCH 1/4] cpufreq: stats: Defer stats update to cpufreq_stats_record

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Message-ID: <20200911113532.zq2bou4swixb2ymk@vireshk-i7>
Date:   Fri, 11 Sep 2020 17:05:32 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     peterz@...radead.org
Cc:     Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lukasz Luba <lukasz.luba@....com>, cristian.marussi@....com,
        sudeep.holla@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] cpufreq: stats: Defer stats update to
 cpufreq_stats_record_transition()

On 11-09-20, 12:11, peterz@...radead.org wrote:
> On Wed, Sep 02, 2020 at 12:54:41PM +0530, Viresh Kumar wrote:
> > +	atomic_t reset_pending;
> 
> > +	atomic_set(&stats->reset_pending, 0);
> > +	if (atomic_read(&stats->reset_pending))
> > +	bool pending = atomic_read(&stats->reset_pending);
> > +	atomic_set(&stats->reset_pending, 1);
> > +	bool pending = atomic_read(&stats->reset_pending);
> > +	if (atomic_read(&stats->reset_pending))
> 
> What do you think atomic_t is doing for you?

I was trying to avoid races while two writes are going in parallel,
but obviously as this isn't a RMW operation, it won't result in
anything for me.

Maybe what I should be doing is just READ_ONCE()/WRITE_ONCE()? So the
other side doesn't see any intermediate value that was never meant to
be set/read ?

-- 
viresh