Re: [PATCH] PM: EM: Rank boost and non-boost frequencies separately

[Lukasz Luba <lukasz.luba@arm.com>]

On 10/30/26 08:10, Guo Chen wrote:
> em_compute_costs() ranks all the frequencies of the table, boost ones
> included. A non-boost frequency can be marked inefficient only because
> a faster boost frequency has a lower or equal cost, e.g.
> 
>    3.9 GHz  4.0 GHz (cost C)  4.1 GHz (boost, cost C)
> 
> With boost disabled 4.1 GHz cannot be selected, but 4.0 GHz is still
> skipped by governors rounding down to efficient frequencies (e.g.
> ondemand with CPUFREQ_RELATION_HE), which land on 3.9 GHz instead of
> the best selectable frequency. Several frequencies can be affected.
> 
> Rank boost and non-boost frequencies separately in em_compute_costs(),
> using the highest non-boost frequency of the CPUFreq table, returned by
> the new helper cpufreq_table_max_nonboost_freq(), as the boundary.
> 
> Fixes: c8ed99533dbc ("PM: EM: Mark inefficient states")
> Signed-off-by: Guo Chen <guo.chen@oss.qualcomm.com>
> ---
>   include/linux/cpufreq.h     | 24 ++++++++++++++++++++++++
>   kernel/power/energy_model.c | 15 +++++++++++++++
>   2 files changed, 39 insertions(+)
> 
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index d3d0d9d02aa4..c93316141a11 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -1155,6 +1155,24 @@ cpufreq_table_set_inefficient(struct cpufreq_policy *policy,
>   	return -EINVAL;
>   }
>   
> +static inline unsigned int
> +cpufreq_table_max_nonboost_freq(struct cpufreq_policy *policy)
> +{
> +	struct cpufreq_frequency_table *pos;
> +	unsigned int max = 0;
> +
> +	if (!policy->freq_table)
> +		return 0;
> +
> +	/* The table may be unsorted, scan all of it for the highest one. */
> +	cpufreq_for_each_valid_entry(pos, policy->freq_table) {
> +		if (!(pos->flags & CPUFREQ_BOOST_FREQ) && pos->frequency > max)
> +			max = pos->frequency;
> +	}
> +
> +	return max;
> +}
> +
>   static inline int parse_perf_domain(int cpu, const char *list_name,
>   				    const char *cell_name,
>   				    struct of_phandle_args *args)
> @@ -1219,6 +1237,12 @@ cpufreq_table_set_inefficient(struct cpufreq_policy *policy,
>   	return -EINVAL;
>   }
>   
> +static inline unsigned int
> +cpufreq_table_max_nonboost_freq(struct cpufreq_policy *policy)
> +{
> +	return 0;
> +}
> +
>   static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_name,
>   						     const char *cell_name, struct cpumask *cpumask,
>   						     struct of_phandle_args *pargs)
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index d19a65461ae8..253c53ca6a74 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -255,15 +255,30 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table,
>   			    unsigned long flags)
>   {
>   	unsigned long prev_cost = ULONG_MAX;
> +	struct cpufreq_policy *policy;
> +	unsigned int max_nonboost = 0;
> +	bool prev_boost = false;
>   	int i, ret;
>   
>   	/* This is needed only for CPUs and EAS skip other devices */
>   	if (!_is_cpu_device(dev))
>   		return 0;
>   
> +	policy = cpufreq_cpu_get(dev->id);
> +	if (policy) {
> +		max_nonboost = cpufreq_table_max_nonboost_freq(policy);
> +		cpufreq_cpu_put(policy);
> +	}
> +
>   	/* Compute the cost of each performance state. */
>   	for (i = nr_states - 1; i >= 0; i--) {
>   		unsigned long power_res, cost;
> +		bool boost = table[i].frequency > max_nonboost;
> +
> +		if (boost != prev_boost) {

We expect in EM fwk that the frequencies are sorted ascending
and we return error during setup if the driver callback fails
to provide that.
Therefore, in this code we don't have to deal with random
'boost' labels with gaps between.

Let's make all OPPs which are 'boost' equally possible
to reach (at least in theory), so label them as
'efficient'. I think this is fair in 'boosting' case scenario
and energy has not that importance in it.

So simply something like, would be enough IMHO:

if (boost)
	prev_cost = ULONG_MAX;


> +			prev_boost = boost;
> +			prev_cost = ULONG_MAX;
> +		}
>   
>   		if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) {
>   			ret = cb->get_cost(dev, table[i].frequency, &cost);
> 
> ---
> base-commit: f1ac44c32cba88ad65dcecd4a279661d14e93651
> base-tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> change-id: 20261029-em-rank-boost-separately-a7e7c7d78058
> 
> Best regards,
> --
> Guo Chen <guo.chen@oss.qualcomm.com>