linux-kernel - Re: [PATCH v6 04/10] PM / EM: add support for other devices than CPUs in Energy Model

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Message-ID: <ff1c8cc5-f64d-6156-7d30-97b8426c6f99@arm.com>
Date:   Thu, 23 Apr 2020 17:57:45 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
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Subject: Re: [PATCH v6 04/10] PM / EM: add support for other devices than CPUs
 in Energy Model



On 4/23/20 4:12 PM, Daniel Lezcano wrote:
> On Fri, Apr 10, 2020 at 09:42:04AM +0100, Lukasz Luba wrote:
>> Add support for other devices that 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). To track usage
>> of the Energy Model structures, they are protected with kref.
> 
> Why not add the energy model structure in the struct device directly?

Do you mean this structure?
https://elixir.bootlin.com/linux/latest/source/include/linux/device.h#L537

and to put something like:
struct device {
...
	struct dev_pm_domain	*pm_domain;
#ifdef CONFIG_ENERGY_MODEL
	struct em_perf_domain	*em_pd;
#endif
...
};

> 
> For instance for the em_cpu_get() function, the cpu id allows to retrieve the
> cpu device and then from there, the energy model instead of browsing another
> list. The em_device life cycle will be tied to the struct device.

That would be perfect.

> 
> Then when the struct device and the em_device are connected, add the debugfs
> with a struct device list for those which are energy aware, so you end up with
> a structure:
> 
> struct em_device {
> 	struct device *dev;
> 	struct list_head em_dev_list;
> };
> 
> (a global single dentry for debugfs to do a recursive delete is enough).
> 
> Locks when inspecting and add/removal called from the struct device release
> function. So no need of an extra refcounting.
> 
> Does it make sense?
> 

Indeed it looks much cleaner/simpler.

I will try to address this idea and get rid of refcounting.

This should be doable in this patch (4/10). In the v7 I will keep your
ACKs for other patches that you have already commented.

Thank you for your suggestions and review.

Regards,
Lukasz