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SubjectRe: [PATCH 2/3] PM: EM: Make em_cpu_energy() able to return bigger values
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On 25/06/2021 17:26, Lukasz Luba wrote:
> The Energy Model (EM) em_cpu_energy() is responsible for providing good
> estimation regarding CPUs energy. It contains proper data structures which
> are then used during calculation. The values stored in there are in
> milli-Watts precision (or in abstract scale) smaller that 0xffff, which use

I guess you refer to 'if (... || power > EM_MAX_POWER)' check in
em_create_perf_table() [kernel/power/energy_model.c].

> sufficient unsigned long even on 32-bit machines. There are scenarios where
^^^^^^^^^

Can you describe these scenarios better with one example (EAS placement
of an example task on a 2 PD system) which highlights the issue and how
it this patch-set solves it?

In this example you can list all the things which must be there to
create a situation in EAS in which the patch-set helps.

> we would like to provide calculated estimations in a better precision and
> the values might be 1000 times bigger. This patch makes possible to use

Where is this `1000` coming from?

> quite big values for also 32-bit machines.
>
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
> include/linux/energy_model.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 3f221dbf5f95..2016f5a706e0 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -101,7 +101,7 @@ void em_dev_unregister_perf_domain(struct device *dev);
> * Return: the sum of the energy consumed by the CPUs of the domain assuming
> * a capacity state satisfying the max utilization of the domain.
> */
> -static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
> +static inline u64 em_cpu_energy(struct em_perf_domain *pd,
> unsigned long max_util, unsigned long sum_util,
> unsigned long allowed_cpu_cap)
> {
> @@ -180,7 +180,7 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
> * pd_nrg = ------------------------ (4)
> * scale_cpu
> */
> - return ps->cost * sum_util / scale_cpu;
> + return div_u64((u64)ps->cost * sum_util, scale_cpu);
> }
>
> /**
> @@ -217,7 +217,7 @@ static inline struct em_perf_domain *em_pd_get(struct device *dev)
> {
> return NULL;
> }
> -static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
> +static inline u64 em_cpu_energy(struct em_perf_domain *pd,
> unsigned long max_util, unsigned long sum_util,
> unsigned long allowed_cpu_cap)
> {
>

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