Re: [PATCH v2 06/17] PM: EM: Add update_power() callback for runtime modifications

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Lukasz Luba <lukasz.luba@arm.com>,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	rafael@kernel.org
Cc: rui.zhang@intel.com, amit.kucheria@verdurent.com,
	amit.kachhap@gmail.com, daniel.lezcano@linaro.org,
	viresh.kumar@linaro.org, len.brown@intel.com, pavel@ucw.cz,
	Pierre.Gondois@arm.com, ionela.voinescu@arm.com,
	rostedt@goodmis.org, mhiramat@kernel.org
Subject: Re: [PATCH v2 06/17] PM: EM: Add update_power() callback for runtime modifications
Date: Tue, 30 May 2023 11:31:34 +0200	[thread overview]
Message-ID: <70e630b8-e577-a148-0179-61aedf910c09@arm.com> (raw)
In-Reply-To: <20230512095743.3393563-7-lukasz.luba@arm.com>

On 12/05/2023 11:57, Lukasz Luba wrote:
> The Energy Model (EM) is going to support runtime modifications. This
> new callback would be used in the upcoming EM changes. The drivers
> or frameworks which want to modify the EM have to implement the
> update_power() callback and provide it via EM API
> em_dev_update_perf_domain(). The callback is then used by the EM
> framework to get new power values for each frequency in existing EM.

Do we have any numbers or feedback that the chosen design (i.e. update
per performance state through update_power()) is performant enough for
the anticipated use case on real devices?

> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  include/linux/energy_model.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 8069f526c9d8..cc2bf607191e 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -158,6 +158,26 @@ struct em_data_callback {
>  	 */
>  	int (*get_cost)(struct device *dev, unsigned long freq,
>  			unsigned long *cost);
> +
> +	/**
> +	 * update_power() - Provide new power at the given performance state of
> +	 *		a device
> +	 * @dev		: Device for which we do this operation (can be a CPU)
> +	 * @freq	: Frequency at the performance state in kHz
> +	 * @power	: New power value at the performance state
> +	 *		(modified)
> +	 * @priv	: Pointer to private data useful for tracking context
> +	 *		during run-time modifications of EM.
> +	 *
> +	 * The update_power() is used by run-time modifiable EM. It aims to
> +	 * provide updated power value for a given frequency, which is stored
> +	 * in the performance state. The power value provided by this callback
> +	 * should fit in the [0, EM_MAX_POWER] range.
> +	 *
> +	 * Return 0 on success, or appropriate error value in case of failure.
> +	 */
> +	int (*update_power)(struct device *dev, unsigned long freq,
> +			    unsigned long *power, void *priv);
>  };
>  #define EM_SET_ACTIVE_POWER_CB(em_cb, cb) ((em_cb).active_power = cb)
>  #define EM_ADV_DATA_CB(_active_power_cb, _cost_cb)	\
> @@ -165,6 +185,7 @@ struct em_data_callback {
>  	  .get_cost = _cost_cb }
>  #define EM_DATA_CB(_active_power_cb)			\
>  		EM_ADV_DATA_CB(_active_power_cb, NULL)
> +#define EM_UPDATE_CB(_update_power_cb) { .update_power = &_update_power_cb }
>  
>  struct em_perf_domain *em_cpu_get(int cpu);
>  struct em_perf_domain *em_pd_get(struct device *dev);