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Message-ID: <20240205074124.sgmjjyfkjb7ozche@vireshk-i7>
Date: Mon, 5 Feb 2024 13:11:24 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] sched: cpufreq: Rename map_util_perf to
apply_dvfs_headroom
On 05-02-24, 02:20, Qais Yousef 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 sched.h. This function relies on updating util signal
> appropriately to give a headroom to grow. This is more of a scheduler
> functionality than cpufreq. Move it to sched.h where all the other util
> handling code belongs.
>
> Signed-off-by: Qais Yousef <qyousef@...alina.io>
> ---
> include/linux/sched/cpufreq.h | 5 -----
> kernel/sched/cpufreq_schedutil.c | 2 +-
> kernel/sched/sched.h | 17 +++++++++++++++++
> 3 files changed, 18 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 95c3c097083e..abbd1ddb0359 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -179,7 +179,7 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> unsigned long max)
> {
> /* Add dvfs headroom to actual utilization */
> - actual = map_util_perf(actual);
> + actual = apply_dvfs_headroom(actual);
> /* Actually we don't need to target the max performance */
> if (actual < max)
> max = actual;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index e58a54bda77d..0da3425200b1 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3002,6 +3002,23 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> unsigned long min,
> unsigned long max);
>
> +/*
> + * 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 apply_dvfs_headroom(unsigned long util)
> +{
> + return util + (util >> 2);
> +}
>
> /*
> * Verify the fitness of task @p to run on @cpu taking into account the
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
--
viresh
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