linux-kernel - Re: [PATCH 1/4] PM / EM: and devices to Energy Model

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Message-ID: <17b77e0c-9455-0479-d37b-c57717c784c7@arm.com>
Date:   Mon, 20 Jan 2020 15:53:35 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     lukasz.luba@....com, 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:     Morten.Rasmussen@....com, Chris.Redpath@....com,
        ionela.voinescu@....com, javi.merino@....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,
        daniel.lezcano@...aro.org, 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, kernel@...gutronix.de, khilman@...nel.org,
        agross@...nel.org, 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, patrick.bellasi@...bug.net
Subject: Re: [PATCH 1/4] PM / EM: and devices to Energy Model

On 16/01/2020 16:20, lukasz.luba@....com wrote:
> From: Lukasz Luba <lukasz.luba@....com>
> 
> Add support of other devices into the Energy Model framework not only the
> CPUs. Change the interface to be more unified which can handle other
> devices as well.

[...]

> -The source of the information about the power consumed by CPUs can vary greatly
> +The source of the information about the power consumed by devices can vary greatly
>  from one platform to another. These power costs can be estimated using
>  devicetree data in some cases. In others, the firmware will know better.
>  Alternatively, userspace might be best positioned. And so on. In order to avoid
> @@ -26,7 +28,7 @@ framework, and interested clients reading the data from it::
>         | Thermal (IPA) |  | Scheduler (EAS) |  |     Other     |
>         +---------------+  +-----------------+  +---------------+
>                 |                   | em_pd_energy()    |
> -               |                   | em_cpu_get()      |
> +               |  em_dev_get()     | em_cpu_get()      |

Looked really hard but can't find a em_dev_get() in the code? You mean
em_get_pd() ? And why em_get_pd() and not em_pd_get()?

>                 +---------+         |         +---------+
>                           |         |         |
>                           v         v         v
> @@ -47,12 +49,12 @@ framework, and interested clients reading the data from it::
>          | Device Tree  |   |   Firmware    |  |      ?       |
>          +--------------+   +---------------+  +--------------+

[...]

> +There is two API functions which provide the access to the energy model:
> +em_cpu_get() which takes CPU id as an argument and em_dev_get() with device
> +pointer as an argument. It depends on the subsystem which interface it is
> +going to use.

Would be really nice if this wouldn't be required. We should really aim
for 1 framework == 1 set of interfaces.

What happens if someone calls em_get_pd() on a CPU EM?

E.g:

 static struct perf_domain *pd_init(int cpu)
 {
-       struct em_perf_domain *obj = em_cpu_get(cpu);
+       struct device *dev = get_cpu_device(cpu);
+       struct em_perf_domain *obj = em_pd_get(dev);
        struct perf_domain *pd;

Two versions of one functionality will confuse API user from the
beginning ...

[...]

> +enum em_type {
> +	EM_SIMPLE,
> +	EM_CPU,
> +};

s/EM_SIMPLE/EM_DEV ?

Right now I only see energy models and _one_ specific type (the CPU EM).
So a tag 'is a CPU EM' would suffice. No need for EM_SIMPE ...

[...]