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Date: Wed, 7 Oct 2020 16:12:25 +0100
From: Ionela Voinescu <ionela.voinescu@....com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
dri-devel@...ts.freedesktop.org, amit.kucheria@...durent.com,
airlied@...ux.ie, daniel.lezcano@...aro.org, steven.price@....com,
alyssa.rosenzweig@...labora.com, rui.zhang@...el.com,
orjan.eide@....com
Subject: Re: [PATCH 4/5] thermal: devfreq_cooling: remove old power model and
use EM
Hi Lukasz,
On Monday 21 Sep 2020 at 13:20:06 (+0100), Lukasz Luba wrote:
[..]
> /**
> - * freq_get_state() - get the cooling state corresponding to a frequency
> + * freq_get_state() - get the performance index corresponding to a frequency
If we change the meaning of the return value, I think the function needs
a name change as well.
Also, we do treat this as a cooling state when we do validation and
compare it to THERMAL_CSTATE_INVALID, but it's not actually a cooling
state (it's max_state - state). It does create confusion if we name
"state" both a performance index and a cooling state.
Given that the only user is devfreq_cooling_get_requested_power(),
might be good to collapse freq_get_state() in that function and rename
the "state" variable in there to "em_perf_idx".
> * @dfc: Pointer to devfreq cooling device
> - * @freq: frequency in Hz
> + * @freq: frequency in kHz
> *
> - * Return: the cooling state associated with the @freq, or
> + * Return: the performance index associated with the @freq, or
> * THERMAL_CSTATE_INVALID if it wasn't found.
> */
> static unsigned long
> @@ -128,8 +130,8 @@ freq_get_state(struct devfreq_cooling_device *dfc, unsigned long freq)
> {
> int i;
>
> - for (i = 0; i < dfc->freq_table_size; i++) {
> - if (dfc->freq_table[i] == freq)
> + for (i = 0; i <= dfc->max_state; i++) {
> + if (dfc->em->table[i].frequency == freq)
> return i;
> }
>
> @@ -164,71 +166,15 @@ static unsigned long get_voltage(struct devfreq *df, unsigned long freq)
> return voltage;
> }
>
> -/**
> - * get_static_power() - calculate the static power
> - * @dfc: Pointer to devfreq cooling device
> - * @freq: Frequency in Hz
> - *
> - * Calculate the static power in milliwatts using the supplied
> - * get_static_power(). The current voltage is calculated using the
> - * OPP library. If no get_static_power() was supplied, assume the
> - * static power is negligible.
> - */
> -static unsigned long
> -get_static_power(struct devfreq_cooling_device *dfc, unsigned long freq)
> +static void dfc_em_get_requested_power(struct em_perf_domain *em,
> + struct devfreq_dev_status *status,
> + u32 *power, int em_perf_idx)
Is there a reason for not directly returning the power value in this
function? Also, this only does a few arithmetic operations and it's only
called in one place. Is it worth to have this in a separate function?
[..]
> @@ -345,11 +279,8 @@ static int devfreq_cooling_power2state(struct thermal_cooling_device *cdev,
> struct devfreq_cooling_device *dfc = cdev->devdata;
> struct devfreq *df = dfc->devfreq;
> struct devfreq_dev_status status;
> - unsigned long busy_time;
> + u32 est_power = power;
Nit: You could use power directly and remove est_power as well.
> unsigned long freq;
> - s32 dyn_power;
> - u32 static_power;
> - s32 est_power;
> int i;
>
> mutex_lock(&df->lock);
> @@ -358,31 +289,26 @@ static int devfreq_cooling_power2state(struct thermal_cooling_device *cdev,
>
> freq = status.current_frequency;
>
> - if (dfc->power_ops->get_real_power) {
> + if (dfc->power_ops && dfc->power_ops->get_real_power) {
> /* Scale for resource utilization */
> est_power = power * dfc->res_util;
> est_power /= SCALE_ERROR_MITIGATION;
> } else {
> - static_power = get_static_power(dfc, freq);
> -
> - dyn_power = power - static_power;
> - dyn_power = dyn_power > 0 ? dyn_power : 0;
> -
> - /* Scale dynamic power for utilization */
> - busy_time = status.busy_time ?: 1;
> - est_power = (dyn_power * status.total_time) / busy_time;
> + _normalize_load(&status);
> + est_power *= status.total_time;
> + est_power /= status.busy_time;
> }
>
> /*
> * Find the first cooling state that is within the power
> - * budget for dynamic power.
> + * budget. The EM power table is sorted ascending.
> */
> - for (i = 0; i < dfc->freq_table_size - 1; i++)
> - if (est_power >= dfc->power_table[i])
> + for (i = dfc->max_state; i > 0; i--)
> + if (est_power >= dfc->em->table[i].power)
> break;
>
> - *state = i;
> - dfc->capped_state = i;
> + *state = dfc->max_state - i;
> + dfc->capped_state = *state;
> trace_thermal_power_devfreq_limit(cdev, freq, *state, power);
> return 0;
> }
[..]
> /**
> @@ -503,7 +381,7 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
> struct thermal_cooling_device *cdev;
> struct devfreq_cooling_device *dfc;
> char dev_name[THERMAL_NAME_LENGTH];
> - int err;
> + int err, num_opps;
>
> dfc = kzalloc(sizeof(*dfc), GFP_KERNEL);
> if (!dfc)
> @@ -511,28 +389,45 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
>
> dfc->devfreq = df;
>
> - if (dfc_power) {
> - dfc->power_ops = dfc_power;
> -
> + dfc->em = em_pd_get(df->dev.parent);
> + if (dfc->em) {
> devfreq_cooling_ops.get_requested_power =
> devfreq_cooling_get_requested_power;
> devfreq_cooling_ops.state2power = devfreq_cooling_state2power;
> devfreq_cooling_ops.power2state = devfreq_cooling_power2state;
> +
> + dfc->power_ops = dfc_power;
> +
> + num_opps = em_pd_nr_perf_states(dfc->em);
> + } else {
> + /* Backward compatibility for drivers which do not use IPA */
> + dev_dbg(df->dev.parent, "missing EM for cooling device\n");
> +
> + num_opps = dev_pm_opp_get_opp_count(df->dev.parent);
> +
> + err = devfreq_cooling_gen_tables(dfc, num_opps);
> + if (err)
> + goto free_dfc;
> }
>
> - err = devfreq_cooling_gen_tables(dfc);
> - if (err)
> + if (num_opps <= 0) {
> + err = -EINVAL;
> goto free_dfc;
> + }
> +
> + /* max_state is an index, not a counter */
Nit: Might be more clear to replace "index" with cooling state. Then
knowledge about cooling states would make this more clear.
Regards,
Ionela.
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