Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle injection
 framework
To:     Peter Zijlstra <peterz@infradead.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>
References: <1528190208-22915-1-git-send-email-daniel.lezcano@linaro.org>
 <20180606122357.GN12258@hirez.programming.kicks-ass.net>
 <22f5cf0b-049e-7938-55f6-4b4b154f8389@linaro.org>
 <20180606150203.GE12180@hirez.programming.kicks-ass.net>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <ea347237-7cef-095a-5ddb-19c181d10c23@linaro.org>
Date:   Thu, 7 Jun 2018 10:18:27 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <20180606150203.GE12180@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 ?


-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog