Re: [PATCH v2] sched: cpufreq: Rename map_util_perf to sugov_apply_dvfs_headroom

[Vincent Guittot]

On Tue, 20 Feb 2024 at 19:08, Qais Yousef <qyousef@xxxxxxxxxxx> wrote:
>
> We are providing headroom for the utilization to grow until the next
> decision point to pick the next frequency. Give the function a better
> name and give it some documentation. It is not really mapping anything.
>
> Also move it to cpufreq_schedutil.c. This function relies on updating
> util signal appropriately to give a headroom to grow. This is tied to
> schedutil and scheduler and not something that can be shared with other
> governors.
>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Signed-off-by: Qais Yousef <qyousef@xxxxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
>
> Changes in v2:
>
>         1. Add Acked-by from Viresh and Raphael (Thanks!)
>         2. Move the function to cpufreq_schedutil.c instead of sched.h
>         3. Name space the function with sugov_ to indicate it is special to
>            this governor only and not generic.
>
>  include/linux/sched/cpufreq.h    |  5 -----
>  kernel/sched/cpufreq_schedutil.c | 20 +++++++++++++++++++-
>  2 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index bdd31ab93bc5..d01755d3142f 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
>  {
>         return freq * util / cap;
>  }
> -
> -static inline unsigned long map_util_perf(unsigned long util)
> -{
> -       return util + (util >> 2);
> -}
>  #endif /* CONFIG_CPU_FREQ */
>
>  #endif /* _LINUX_SCHED_CPUFREQ_H */
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index eece6244f9d2..575df3599813 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -178,12 +178,30 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>         return cpufreq_driver_resolve_freq(policy, freq);
>  }
>
> +/*
> + * DVFS decision are made at discrete points. If CPU stays busy, the util will
> + * continue to grow, which means it could need to run at a higher frequency
> + * before the next decision point was reached. IOW, we can't follow the util as
> + * it grows immediately, but there's a delay before we issue a request to go to
> + * higher frequency. The headroom caters for this delay so the system continues
> + * to run at adequate performance point.
> + *
> + * This function provides enough headroom to provide adequate performance
> + * assuming the CPU continues to be busy.
> + *
> + * At the moment it is a constant multiplication with 1.25.
> + */
> +static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util)
> +{
> +       return util + (util >> 2);
> +}
> +
>  unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
>                                  unsigned long min,
>                                  unsigned long max)
>  {
>         /* Add dvfs headroom to actual utilization */
> -       actual = map_util_perf(actual);
> +       actual = sugov_apply_dvfs_headroom(actual);
>         /* Actually we don't need to target the max performance */
>         if (actual < max)
>                 max = actual;
> --
> 2.34.1
>