linux-kernel - Re: [PATCH v8 4/8] PM / EM: add support for other devices than CPUs in Energy Model

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Message-ID: <7201e161-6952-6e28-4036-bd0f0353ec30@arm.com>
Date:   Tue, 2 Jun 2020 12:31:25 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-imx@....com
Cc:     Dietmar.Eggemann@....com, cw00.choi@...sung.com,
        b.zolnierkie@...sung.com, rjw@...ysocki.net, sudeep.holla@....com,
        viresh.kumar@...aro.org, nm@...com, sboyd@...nel.org,
        rui.zhang@...el.com, amit.kucheria@...durent.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        qperret@...gle.com, bsegall@...gle.com, mgorman@...e.de,
        shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com,
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        bjorn.andersson@...aro.org, robh@...nel.org,
        matthias.bgg@...il.com, steven.price@....com,
        tomeu.vizoso@...labora.com, alyssa.rosenzweig@...labora.com,
        airlied@...ux.ie, daniel@...ll.ch, liviu.dudau@....com,
        lorenzo.pieralisi@....com, patrick.bellasi@...bug.net,
        orjan.eide@....com, rdunlap@...radead.org, mka@...omium.org
Subject: Re: [PATCH v8 4/8] PM / EM: add support for other devices than CPUs
 in Energy Model

Hi Daniel,

On 6/1/20 10:44 PM, Daniel Lezcano wrote:
> On 27/05/2020 11:58, Lukasz Luba wrote:
>> Add support for other devices than CPUs. The registration function
>> does not require a valid cpumask pointer and is ready to handle new
>> devices. Some of the internal structures has been reorganized in order to
>> keep consistent view (like removing per_cpu pd pointers).
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
> 
> [ ... ]
> 
>>   }
>>   EXPORT_SYMBOL_GPL(em_register_perf_domain);
>> +
>> +/**
>> + * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device
>> + * @dev		: Device for which the EM is registered
>> + *
>> + * Try to unregister the EM for the specified device (but not a CPU).
>> + */
>> +void em_dev_unregister_perf_domain(struct device *dev)
>> +{
>> +	if (IS_ERR_OR_NULL(dev) || !dev->em_pd)
>> +		return;
>> +
>> +	if (_is_cpu_device(dev))
>> +		return;
>> +
>> +	mutex_lock(&em_pd_mutex);
> 
> Is the mutex really needed?

I just wanted to align this unregister code with register. Since there
is debugfs dir lookup and the device's EM existence checks I thought it
wouldn't harm just to lock for a while and make sure the registration
path is not used. These two paths shouldn't affect each other, but with
modules loading/unloading I wanted to play safe.
I can change it maybe to just dmb() and the end of the function if it's
a big performance problem in this unloading path. What do you think?

> 
> If this function is called that means there is no more user of the
> em_pd, no?

True, that EM users should already be unregistered i.e. thermal cooling.

> 
>> +	em_debug_remove_pd(dev);
>> +
>> +	kfree(dev->em_pd->table);
>> +	kfree(dev->em_pd);
>> +	dev->em_pd = NULL;
>> +	mutex_unlock(&em_pd_mutex);
>> +}
>> +EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);
>>
> 
> 

Thank you for reviewing this.

Regards,
Lukasz