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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Tue, 31 May 2022 09:59:01 +0200
Message-ID: <CAKfTPtDiRWa5Gu1Xa6k=Yp+6AhNz3d-9xXhJY-JjzU0+anOHig@mail.gmail.com>
Subject: Re: [PATCH v9 3/7] sched, drivers: Remove max param from effective_cpu_util()/sched_cpu_util()
To:     Vincent Donnefort <vdonnefort@google.com>
Cc:     peterz@infradead.org, mingo@redhat.com,
        linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com,
        morten.rasmussen@arm.com, chris.redpath@arm.com,
        qperret@google.com, tao.zhou@linux.dev, kernel-team@android.com
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On Mon, 23 May 2022 at 17:52, Vincent Donnefort <vdonnefort@google.com> wrote:
>
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> effective_cpu_util() already has a `int cpu' parameter which allows to
> retrieve the CPU capacity scale factor (or maximum CPU capacity) inside
> this function via an arch_scale_cpu_capacity(cpu).
>
> A lot of code calling effective_cpu_util() (or the shim
> sched_cpu_util()) needs the maximum CPU capacity, i.e. it will call
> arch_scale_cpu_capacity() already.
> But not having to pass it into effective_cpu_util() will make the EAS
> wake-up code easier, especially when the maximum CPU capacity reduced
> by the thermal pressure is passed through the EAS wake-up functions.
>
> Due to the asymmetric CPU capacity support of arm/arm64 architectures,
> arch_scale_cpu_capacity(int cpu) is a per-CPU variable read access via
> per_cpu(cpu_scale, cpu) on such a system.
> On all other architectures it is a a compile-time constant
> (SCHED_CAPACITY_SCALE).
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

Acked-by: Vincent Guittot <vincent.guittot@linaro.org>

>
> diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
> index f5eced0842b3..6a88eb7e9f75 100644
> --- a/drivers/powercap/dtpm_cpu.c
> +++ b/drivers/powercap/dtpm_cpu.c
> @@ -71,34 +71,19 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
>
>  static u64 scale_pd_power_uw(struct cpumask *pd_mask, u64 power)
>  {
> -       unsigned long max = 0, sum_util = 0;
> +       unsigned long max, sum_util = 0;
>         int cpu;
>
> -       for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
> -
> -               /*
> -                * The capacity is the same for all CPUs belonging to
> -                * the same perf domain, so a single call to
> -                * arch_scale_cpu_capacity() is enough. However, we
> -                * need the CPU parameter to be initialized by the
> -                * loop, so the call ends up in this block.
> -                *
> -                * We can initialize 'max' with a cpumask_first() call
> -                * before the loop but the bits computation is not
> -                * worth given the arch_scale_cpu_capacity() just
> -                * returns a value where the resulting assembly code
> -                * will be optimized by the compiler.
> -                */
> -               max = arch_scale_cpu_capacity(cpu);
> -               sum_util += sched_cpu_util(cpu, max);
> -       }
> -
>         /*
> -        * In the improbable case where all the CPUs of the perf
> -        * domain are offline, 'max' will be zero and will lead to an
> -        * illegal operation with a zero division.
> +        * The capacity is the same for all CPUs belonging to
> +        * the same perf domain.
>          */
> -       return max ? (power * ((sum_util << 10) / max)) >> 10 : 0;
> +       max = arch_scale_cpu_capacity(cpumask_first(pd_mask));
> +
> +       for_each_cpu_and(cpu, pd_mask, cpu_online_mask)
> +               sum_util += sched_cpu_util(cpu);
> +
> +       return (power * ((sum_util << 10) / max)) >> 10;
>  }
>
>  static u64 get_pd_power_uw(struct dtpm *dtpm)
> diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
> index b8151d95a806..b263b0fde03c 100644
> --- a/drivers/thermal/cpufreq_cooling.c
> +++ b/drivers/thermal/cpufreq_cooling.c
> @@ -137,11 +137,9 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
>  static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu,
>                     int cpu_idx)
>  {
> -       unsigned long max = arch_scale_cpu_capacity(cpu);
> -       unsigned long util;
> +       unsigned long util = sched_cpu_util(cpu);
>
> -       util = sched_cpu_util(cpu, max);
> -       return (util * 100) / max;
> +       return (util * 100) / arch_scale_cpu_capacity(cpu);
>  }
>  #else /* !CONFIG_SMP */
>  static u32 get_load(struct cpufreq_cooling_device *cpufreq_cdev, int cpu,
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c46f3a63b758..88b8817b827d 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2257,7 +2257,7 @@ static inline bool owner_on_cpu(struct task_struct *owner)
>  }
>
>  /* Returns effective CPU energy utilization, as seen by the scheduler */
> -unsigned long sched_cpu_util(int cpu, unsigned long max);
> +unsigned long sched_cpu_util(int cpu);
>  #endif /* CONFIG_SMP */
>
>  #ifdef CONFIG_RSEQ
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 53596842f0d8..c531976ee960 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7107,12 +7107,14 @@ struct task_struct *idle_task(int cpu)
>   * required to meet deadlines.
>   */
>  unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> -                                unsigned long max, enum cpu_util_type type,
> +                                enum cpu_util_type type,
>                                  struct task_struct *p)
>  {
> -       unsigned long dl_util, util, irq;
> +       unsigned long dl_util, util, irq, max;
>         struct rq *rq = cpu_rq(cpu);
>
> +       max = arch_scale_cpu_capacity(cpu);
> +
>         if (!uclamp_is_used() &&
>             type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
>                 return max;
> @@ -7192,10 +7194,9 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
>         return min(max, util);
>  }
>
> -unsigned long sched_cpu_util(int cpu, unsigned long max)
> +unsigned long sched_cpu_util(int cpu)
>  {
> -       return effective_cpu_util(cpu, cpu_util_cfs(cpu), max,
> -                                 ENERGY_UTIL, NULL);
> +       return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL);
>  }
>  #endif /* CONFIG_SMP */
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 3dbf351d12d5..1207c78f85c1 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -157,11 +157,10 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>  static void sugov_get_util(struct sugov_cpu *sg_cpu)
>  {
>         struct rq *rq = cpu_rq(sg_cpu->cpu);
> -       unsigned long max = arch_scale_cpu_capacity(sg_cpu->cpu);
>
> -       sg_cpu->max = max;
> +       sg_cpu->max = arch_scale_cpu_capacity(sg_cpu->cpu);
>         sg_cpu->bw_dl = cpu_bw_dl(rq);
> -       sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu), max,
> +       sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu),
>                                           FREQUENCY_UTIL, NULL);
>  }
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index df5e6e565b4d..73a9dc522b73 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6703,12 +6703,11 @@ static long
>  compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>  {
>         struct cpumask *pd_mask = perf_domain_span(pd);
> -       unsigned long cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
> -       unsigned long max_util = 0, sum_util = 0;
> -       unsigned long _cpu_cap = cpu_cap;
> +       unsigned long max_util = 0, sum_util = 0, cpu_cap;
>         int cpu;
>
> -       _cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
> +       cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
> +       cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
>
>         /*
>          * The capacity state of CPUs of the current rd can be driven by CPUs
> @@ -6745,10 +6744,10 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>                  * is already enough to scale the EM reported power
>                  * consumption at the (eventually clamped) cpu_capacity.
>                  */
> -               cpu_util = effective_cpu_util(cpu, util_running, cpu_cap,
> -                                             ENERGY_UTIL, NULL);
> +               cpu_util = effective_cpu_util(cpu, util_running, ENERGY_UTIL,
> +                                             NULL);
>
> -               sum_util += min(cpu_util, _cpu_cap);
> +               sum_util += min(cpu_util, cpu_cap);
>
>                 /*
>                  * Performance domain frequency: utilization clamping
> @@ -6757,12 +6756,12 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>                  * NOTE: in case RT tasks are running, by default the
>                  * FREQUENCY_UTIL's utilization can be max OPP.
>                  */
> -               cpu_util = effective_cpu_util(cpu, util_freq, cpu_cap,
> -                                             FREQUENCY_UTIL, tsk);
> -               max_util = max(max_util, min(cpu_util, _cpu_cap));
> +               cpu_util = effective_cpu_util(cpu, util_freq, FREQUENCY_UTIL,
> +                                             tsk);
> +               max_util = max(max_util, min(cpu_util, cpu_cap));
>         }
>
> -       return em_cpu_energy(pd->em_pd, max_util, sum_util, _cpu_cap);
> +       return em_cpu_energy(pd->em_pd, max_util, sum_util, cpu_cap);
>  }
>
>  /*
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 97bc26e5c8af..07b7c50bd987 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2895,7 +2895,7 @@ enum cpu_util_type {
>  };
>
>  unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> -                                unsigned long max, enum cpu_util_type type,
> +                                enum cpu_util_type type,
>                                  struct task_struct *p);
>
>  static inline unsigned long cpu_bw_dl(struct rq *rq)
> --
> 2.36.1.124.g0e6072fb45-goog
>