Re: [PATCH 4/4] energy_model: use a fixed reference frequency

[Ionela Voinescu <ionela.voinescu@arm.com>]

On Friday 01 Sep 2023 at 15:03:12 (+0200), Vincent Guittot wrote:
> The last item of a performance domain is not always the performance point
> that has been used to compute CPU's capacity. This can lead to different
> target frequency compared with other part of the system like schedutil and
> would result in wrong energy estimation.
> 
> a new arch_scale_freq_ref() is available to return a fixed and coherent
> frequency reference that can be used when computing the CPU's frequency
> for an level of utilization. Use this function when available or fallback
> to the last performance domain item otherwise.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  include/linux/energy_model.h | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index b9caa01dfac4..7ee07be6928e 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -204,6 +204,20 @@ struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
>  	return ps;
>  }
>  
> +#ifdef arch_scale_freq_ref
> +static __always_inline
> +unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)

The comments in patch 3/4 should be considered for this function and its
use as well.

Thanks,
Ionela.

> +{
> +	return arch_scale_freq_ref(cpu);
> +}
> +#else
> +static __always_inline
> +unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)
> +{
> +	return pd->table[pd->nr_perf_states - 1].frequency;
> +}
> +#endif
> +
>  /**
>   * em_cpu_energy() - Estimates the energy consumed by the CPUs of a
>   *		performance domain
> @@ -224,7 +238,7 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>  				unsigned long max_util, unsigned long sum_util,
>  				unsigned long allowed_cpu_cap)
>  {
> -	unsigned long freq, scale_cpu;
> +	unsigned long freq, ref_freq, scale_cpu;
>  	struct em_perf_state *ps;
>  	int cpu;
>  
> @@ -241,11 +255,11 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>  	 */
>  	cpu = cpumask_first(to_cpumask(pd->cpus));
>  	scale_cpu = arch_scale_cpu_capacity(cpu);
> -	ps = &pd->table[pd->nr_perf_states - 1];
> +	ref_freq = arch_scale_freq_ref_em(cpu, pd);
>  
>  	max_util = map_util_perf(max_util);
>  	max_util = min(max_util, allowed_cpu_cap);
> -	freq = map_util_freq(max_util, ps->frequency, scale_cpu);
> +	freq = map_util_freq(max_util, ref_freq, scale_cpu);
>  
>  	/*
>  	 * Find the lowest performance state of the Energy Model above the
> -- 
> 2.34.1
> 
>