linux-kernel - Re: [PATCH v2 1/4] PM / EM: add devices to Energy Model

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Date:   Thu, 13 Feb 2020 11:59:59 +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,
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        lorenzo.pieralisi@....com, patrick.bellasi@...bug.net
Subject: Re: [PATCH v2 1/4] PM / EM: add devices to Energy Model

On 06/02/2020 14:46, lukasz.luba@....com wrote:
> From: Lukasz Luba <lukasz.luba@....com>

[..]

> @@ -26,7 +28,7 @@ framework, and interested clients reading the data from it::

s/::/: ?

>         | Thermal (IPA) |  | Scheduler (EAS) |  |     Other     |
>         +---------------+  +-----------------+  +---------------+
>                 |                   | em_pd_energy()    |
> -               |                   | em_cpu_get()      |
> +               |  em_get_pd()      | em_cpu_get()      |
>                 +---------+         |         +---------+

em_get_pd() and em_cpu_get()? Why not em_pd_get()? em_cpu_get() is a
specific em_get_pd(). right?

[...]

> @@ -85,13 +89,20 @@ API.
>  2.3 Accessing performance domains
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>  
> +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_get_pd() with device
> +pointer as an argument. It depends on the subsystem which interface it is
> +going to use, but in case of CPU devices both functions return the same
> +performance domain.

There is probably a reason why we need this specific function for CPU
devices? The reason should be described. People might ask why
em_get_pd() is not sufficient.

[...]

> - * A "performance domain" represents a group of CPUs whose performance is
> - * scaled together. All CPUs of a performance domain must have the same
> - * micro-architecture. Performance domains often have a 1-to-1 mapping with
> - * CPUFreq policies.
> + * In case of CPU device, a "performance domain" represents a group of CPUs
> + * whose performance is scaled together. All CPUs of a performance domain
> + * must have the same micro-architecture. Performance domains often have
> + * a 1-to-1 mapping with CPUFreq policies.
> + * In case of other devices the 'priv' field is unused.
>   */
>  struct em_perf_domain {
> -	struct em_cap_state *table;
> -	int nr_cap_states;
> -	unsigned long cpus[0];
> +	struct em_perf_state *table;
> +	int nr_perf_states;
> +	void *priv;

In case you go back to the variable length field plus type field to
distingush EM devices, keep cpus[0] as the name.

[..]

>  /**
> - * em_pd_energy() - Estimates the energy consumed by the CPUs of a perf. domain
> + * em_pd_energy() - Estimates the energy consumed by the CPUs of a perf.
> +			domain

Why this change?

[...]

> @@ -141,12 +210,12 @@ static struct em_perf_domain *em_create_pd(cpumask_t *span, int nr_states,
>  		 */
>  		opp_eff = freq / power;
>  		if (opp_eff >= prev_opp_eff)
> -			pr_warn("pd%d: hertz/watts ratio non-monotonically decreasing: em_cap_state %d >= em_cap_state%d\n",
> -					cpu, i, i - 1);
> +			dev_warn(dev, "energy_model: hertz/watts ratio non-monotonically decreasing: em_perf_state %d >= em_perf_state%d\n",

s/energy_model/EM ?

[...]