Re: [PATCH v4 1/2] sched/schedutil: Rework performance estimation

[Rafael J. Wysocki]

On Wed, Nov 22, 2023 at 2:39 PM Vincent Guittot
<vincent.guittot@xxxxxxxxxx> wrote:
>
> The current method to take into account uclamp hints when estimating the
> target frequency can end into situation where the selected target
> frequency is finally higher than uclamp hints whereas there are no real
> needs. Such cases mainly happen because we are currently mixing the
> traditional scheduler utilization signal with the uclamp performance
> hints. By adding these 2 metrics, we loose an important information when
> it comes to select the target frequency and we have to make some
> assumptions which can't fit all cases.
>
> Rework the interface between the scheduler and schedutil governor in order
> to propagate all information down to the cpufreq governor.
>
> effective_cpu_util() interface changes and now returns the actual
> utilization of the CPU with 2 optional inputs:
> - The minimum performance for this CPU; typically the capacity to handle
>   the deadline task and the interrupt pressure. But also uclamp_min
>   request when available.
> - The maximum targeting performance for this CPU which reflects the
>   maximum level that we would like to not exceed. By default it will be
>   the CPU capacity but can be reduced because of some performance hints
>   set with uclamp. The value can be lower than actual utilization and/or
>   min performance level.
>
> A new sugov_effective_cpu_perf() interface is also available to compute
> the final performance level that is targeted for the CPU after applying
> some cpufreq headroom and taking into account all inputs.
>
> With these 2 functions, schedutil is now able to decide when it must go
> above uclamp hints. It now also have a generic way to get the min
> perfromance level.
>
> The dependency between energy model and cpufreq governor and its headroom
> policy doesn't exist anymore.
>
> eenv_pd_max_util asks schedutil for the targeted performance after
> applying the impact of the waking task.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>

> ---
>  include/linux/energy_model.h     |  1 -
>  kernel/sched/core.c              | 90 ++++++++++++++------------------
>  kernel/sched/cpufreq_schedutil.c | 35 +++++++++----
>  kernel/sched/fair.c              | 22 ++++++--
>  kernel/sched/sched.h             | 24 +++------
>  5 files changed, 89 insertions(+), 83 deletions(-)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index b9caa01dfac4..adec808b371a 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -243,7 +243,6 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>         scale_cpu = arch_scale_cpu_capacity(cpu);
>         ps = &pd->table[pd->nr_perf_states - 1];
>
> -       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);
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 2de77a6d5ef8..900b5bacb662 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7467,18 +7467,13 @@ int sched_core_idle_cpu(int cpu)
>   * required to meet deadlines.
>   */
>  unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> -                                enum cpu_util_type type,
> -                                struct task_struct *p)
> +                                unsigned long *min,
> +                                unsigned long *max)
>  {
> -       unsigned long dl_util, util, irq, max;
> +       unsigned long util, irq, scale;
>         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;
> -       }
> +       scale = arch_scale_cpu_capacity(cpu);
>
>         /*
>          * Early check to see if IRQ/steal time saturates the CPU, can be
> @@ -7486,45 +7481,49 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
>          * update_irq_load_avg().
>          */
>         irq = cpu_util_irq(rq);
> -       if (unlikely(irq >= max))
> -               return max;
> +       if (unlikely(irq >= scale)) {
> +               if (min)
> +                       *min = scale;
> +               if (max)
> +                       *max = scale;
> +               return scale;
> +       }
> +
> +       if (min) {
> +               /*
> +                * The minimum utilization returns the highest level between:
> +                * - the computed DL bandwidth needed with the irq pressure which
> +                *   steals time to the deadline task.
> +                * - The minimum performance requirement for CFS and/or RT.
> +                */
> +               *min = max(irq + cpu_bw_dl(rq), uclamp_rq_get(rq, UCLAMP_MIN));
> +
> +               /*
> +                * When a RT task is runnable and uclamp is not used, we must
> +                * ensure that the task will run at maximum compute capacity.
> +                */
> +               if (!uclamp_is_used() && rt_rq_is_runnable(&rq->rt))
> +                       *min = max(*min, scale);
> +       }
>
>         /*
>          * Because the time spend on RT/DL tasks is visible as 'lost' time to
>          * CFS tasks and we use the same metric to track the effective
>          * utilization (PELT windows are synchronized) we can directly add them
>          * to obtain the CPU's actual utilization.
> -        *
> -        * CFS and RT utilization can be boosted or capped, depending on
> -        * utilization clamp constraints requested by currently RUNNABLE
> -        * tasks.
> -        * When there are no CFS RUNNABLE tasks, clamps are released and
> -        * frequency will be gracefully reduced with the utilization decay.
>          */
>         util = util_cfs + cpu_util_rt(rq);
> -       if (type == FREQUENCY_UTIL)
> -               util = uclamp_rq_util_with(rq, util, p);
> -
> -       dl_util = cpu_util_dl(rq);
> +       util += cpu_util_dl(rq);
>
>         /*
> -        * For frequency selection we do not make cpu_util_dl() a permanent part
> -        * of this sum because we want to use cpu_bw_dl() later on, but we need
> -        * to check if the CFS+RT+DL sum is saturated (ie. no idle time) such
> -        * that we select f_max when there is no idle time.
> -        *
> -        * NOTE: numerical errors or stop class might cause us to not quite hit
> -        * saturation when we should -- something for later.
> +        * The maximum hint is a soft bandwidth requirement which can be lower
> +        * than the actual utilization because of uclamp_max requirements
>          */
> -       if (util + dl_util >= max)
> -               return max;
> +       if (max)
> +               *max = min(scale, uclamp_rq_get(rq, UCLAMP_MAX));
>
> -       /*
> -        * OTOH, for energy computation we need the estimated running time, so
> -        * include util_dl and ignore dl_bw.
> -        */
> -       if (type == ENERGY_UTIL)
> -               util += dl_util;
> +       if (util >= scale)
> +               return scale;
>
>         /*
>          * There is still idle time; further improve the number by using the
> @@ -7535,28 +7534,15 @@ unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
>          *   U' = irq + --------- * U
>          *                 max
>          */
> -       util = scale_irq_capacity(util, irq, max);
> +       util = scale_irq_capacity(util, irq, scale);
>         util += irq;
>
> -       /*
> -        * Bandwidth required by DEADLINE must always be granted while, for
> -        * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
> -        * to gracefully reduce the frequency when no tasks show up for longer
> -        * periods of time.
> -        *
> -        * Ideally we would like to set bw_dl as min/guaranteed freq and util +
> -        * bw_dl as requested freq. However, cpufreq is not yet ready for such
> -        * an interface. So, we only do the latter for now.
> -        */
> -       if (type == FREQUENCY_UTIL)
> -               util += cpu_bw_dl(rq);
> -
> -       return min(max, util);
> +       return min(scale, util);
>  }
>
>  unsigned long sched_cpu_util(int cpu)
>  {
> -       return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL);
> +       return effective_cpu_util(cpu, cpu_util_cfs(cpu), NULL, NULL);
>  }
>  #endif /* CONFIG_SMP */
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 5888176354e2..f3acf2cf26ed 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -47,7 +47,7 @@ struct sugov_cpu {
>         u64                     last_update;
>
>         unsigned long           util;
> -       unsigned long           bw_dl;
> +       unsigned long           bw_min;
>
>         /* The field below is for single-CPU policies only: */
>  #ifdef CONFIG_NO_HZ_COMMON
> @@ -143,7 +143,6 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>         unsigned int freq = arch_scale_freq_invariant() ?
>                                 policy->cpuinfo.max_freq : policy->cur;
>
> -       util = map_util_perf(util);
>         freq = map_util_freq(util, freq, max);
>
>         if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> @@ -153,14 +152,30 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>         return cpufreq_driver_resolve_freq(policy, freq);
>  }
>
> +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);
> +       /* Actually we don't need to target the max performance */
> +       if (actual < max)
> +               max = actual;
> +
> +       /*
> +        * Ensure at least minimum performance while providing more compute
> +        * capacity when possible.
> +        */
> +       return max(min, max);
> +}
> +
>  static void sugov_get_util(struct sugov_cpu *sg_cpu)
>  {
> -       unsigned long util = cpu_util_cfs_boost(sg_cpu->cpu);
> -       struct rq *rq = cpu_rq(sg_cpu->cpu);
> +       unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
>
> -       sg_cpu->bw_dl = cpu_bw_dl(rq);
> -       sg_cpu->util = effective_cpu_util(sg_cpu->cpu, util,
> -                                         FREQUENCY_UTIL, NULL);
> +       util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
> +       sg_cpu->bw_min = min;
> +       sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
>  }
>
>  /**
> @@ -306,7 +321,7 @@ static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
>   */
>  static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu)
>  {
> -       if (cpu_bw_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->bw_dl)
> +       if (cpu_bw_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->bw_min)
>                 sg_cpu->sg_policy->limits_changed = true;
>  }
>
> @@ -407,8 +422,8 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
>             sugov_cpu_is_busy(sg_cpu) && sg_cpu->util < prev_util)
>                 sg_cpu->util = prev_util;
>
> -       cpufreq_driver_adjust_perf(sg_cpu->cpu, map_util_perf(sg_cpu->bw_dl),
> -                                  map_util_perf(sg_cpu->util), max_cap);
> +       cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
> +                                  sg_cpu->util, max_cap);
>
>         sg_cpu->sg_policy->last_freq_update_time = time;
>  }
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 07f555857698..53e7bf2ccc44 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7780,7 +7780,7 @@ static inline void eenv_pd_busy_time(struct energy_env *eenv,
>         for_each_cpu(cpu, pd_cpus) {
>                 unsigned long util = cpu_util(cpu, p, -1, 0);
>
> -               busy_time += effective_cpu_util(cpu, util, ENERGY_UTIL, NULL);
> +               busy_time += effective_cpu_util(cpu, util, NULL, NULL);
>         }
>
>         eenv->pd_busy_time = min(eenv->pd_cap, busy_time);
> @@ -7803,7 +7803,7 @@ eenv_pd_max_util(struct energy_env *eenv, struct cpumask *pd_cpus,
>         for_each_cpu(cpu, pd_cpus) {
>                 struct task_struct *tsk = (cpu == dst_cpu) ? p : NULL;
>                 unsigned long util = cpu_util(cpu, p, dst_cpu, 1);
> -               unsigned long eff_util;
> +               unsigned long eff_util, min, max;
>
>                 /*
>                  * Performance domain frequency: utilization clamping
> @@ -7812,7 +7812,23 @@ eenv_pd_max_util(struct energy_env *eenv, struct cpumask *pd_cpus,
>                  * NOTE: in case RT tasks are running, by default the
>                  * FREQUENCY_UTIL's utilization can be max OPP.
>                  */
> -               eff_util = effective_cpu_util(cpu, util, FREQUENCY_UTIL, tsk);
> +               eff_util = effective_cpu_util(cpu, util, &min, &max);
> +
> +               /* Task's uclamp can modify min and max value */
> +               if (tsk && uclamp_is_used()) {
> +                       min = max(min, uclamp_eff_value(p, UCLAMP_MIN));
> +
> +                       /*
> +                        * If there is no active max uclamp constraint,
> +                        * directly use task's one otherwise keep max
> +                        */
> +                       if (uclamp_rq_is_idle(cpu_rq(cpu)))
> +                               max = uclamp_eff_value(p, UCLAMP_MAX);
> +                       else
> +                               max = max(max, uclamp_eff_value(p, UCLAMP_MAX));
> +               }
> +
> +               eff_util = sugov_effective_cpu_perf(cpu, eff_util, min, max);
>                 max_util = max(max_util, eff_util);
>         }
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 8a70d51ffa33..c1574cd388e7 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2994,24 +2994,14 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
>  #endif
>
>  #ifdef CONFIG_SMP
> -/**
> - * enum cpu_util_type - CPU utilization type
> - * @FREQUENCY_UTIL:    Utilization used to select frequency
> - * @ENERGY_UTIL:       Utilization used during energy calculation
> - *
> - * The utilization signals of all scheduling classes (CFS/RT/DL) and IRQ time
> - * need to be aggregated differently depending on the usage made of them. This
> - * enum is used within effective_cpu_util() to differentiate the types of
> - * utilization expected by the callers, and adjust the aggregation accordingly.
> - */
> -enum cpu_util_type {
> -       FREQUENCY_UTIL,
> -       ENERGY_UTIL,
> -};
> -
>  unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
> -                                enum cpu_util_type type,
> -                                struct task_struct *p);
> +                                unsigned long *min,
> +                                unsigned long *max);
> +
> +unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> +                                unsigned long min,
> +                                unsigned long max);
> +
>
>  /*
>   * Verify the fitness of task @p to run on @cpu taking into account the
> --
> 2.34.1
>