Re: [PATCH v4 2/2] sched/schedutil: Rework iowait boost

[Rafael J. Wysocki]

On Wed, Nov 22, 2023 at 2:39 PM Vincent Guittot
<vincent.guittot@xxxxxxxxxx> wrote:
>
> Use the max value that has already been computed inside sugov_get_util()
> to cap the iowait boost and remove dependency with uclamp_rq_util_with()
> which is not used anymore.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

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

Or if you want me to pick up this series, please let me know.

> ---
>  kernel/sched/cpufreq_schedutil.c | 29 ++++++++-------
>  kernel/sched/sched.h             | 60 --------------------------------
>  2 files changed, 14 insertions(+), 75 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index f3acf2cf26ed..4ee8ad70be99 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -169,11 +169,12 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
>         return max(min, max);
>  }
>
> -static void sugov_get_util(struct sugov_cpu *sg_cpu)
> +static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
>  {
>         unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
>
>         util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
> +       util = max(util, boost);
>         sg_cpu->bw_min = min;
>         sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
>  }
> @@ -266,18 +267,16 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
>   * This mechanism is designed to boost high frequently IO waiting tasks, while
>   * being more conservative on tasks which does sporadic IO operations.
>   */
> -static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> +static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
>                                unsigned long max_cap)
>  {
> -       unsigned long boost;
> -
>         /* No boost currently required */
>         if (!sg_cpu->iowait_boost)
> -               return;
> +               return 0;
>
>         /* Reset boost if the CPU appears to have been idle enough */
>         if (sugov_iowait_reset(sg_cpu, time, false))
> -               return;
> +               return 0;
>
>         if (!sg_cpu->iowait_boost_pending) {
>                 /*
> @@ -286,7 +285,7 @@ static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
>                 sg_cpu->iowait_boost >>= 1;
>                 if (sg_cpu->iowait_boost < IOWAIT_BOOST_MIN) {
>                         sg_cpu->iowait_boost = 0;
> -                       return;
> +                       return 0;
>                 }
>         }
>
> @@ -296,10 +295,7 @@ static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
>          * sg_cpu->util is already in capacity scale; convert iowait_boost
>          * into the same scale so we can compare.
>          */
> -       boost = (sg_cpu->iowait_boost * max_cap) >> SCHED_CAPACITY_SHIFT;
> -       boost = uclamp_rq_util_with(cpu_rq(sg_cpu->cpu), boost, NULL);
> -       if (sg_cpu->util < boost)
> -               sg_cpu->util = boost;
> +       return (sg_cpu->iowait_boost * max_cap) >> SCHED_CAPACITY_SHIFT;
>  }
>
>  #ifdef CONFIG_NO_HZ_COMMON
> @@ -329,6 +325,8 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
>                                               u64 time, unsigned long max_cap,
>                                               unsigned int flags)
>  {
> +       unsigned long boost;
> +
>         sugov_iowait_boost(sg_cpu, time, flags);
>         sg_cpu->last_update = time;
>
> @@ -337,8 +335,8 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
>         if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
>                 return false;
>
> -       sugov_get_util(sg_cpu);
> -       sugov_iowait_apply(sg_cpu, time, max_cap);
> +       boost = sugov_iowait_apply(sg_cpu, time, max_cap);
> +       sugov_get_util(sg_cpu, boost);
>
>         return true;
>  }
> @@ -439,9 +437,10 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>
>         for_each_cpu(j, policy->cpus) {
>                 struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
> +               unsigned long boost;
>
> -               sugov_get_util(j_sg_cpu);
> -               sugov_iowait_apply(j_sg_cpu, time, max_cap);
> +               boost = sugov_iowait_apply(j_sg_cpu, time, max_cap);
> +               sugov_get_util(j_sg_cpu, boost);
>
>                 util = max(j_sg_cpu->util, util);
>         }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index c1574cd388e7..e58a54bda77d 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3058,59 +3058,6 @@ static inline bool uclamp_rq_is_idle(struct rq *rq)
>         return rq->uclamp_flags & UCLAMP_FLAG_IDLE;
>  }
>
> -/**
> - * uclamp_rq_util_with - clamp @util with @rq and @p effective uclamp values.
> - * @rq:                The rq to clamp against. Must not be NULL.
> - * @util:      The util value to clamp.
> - * @p:         The task to clamp against. Can be NULL if you want to clamp
> - *             against @rq only.
> - *
> - * Clamps the passed @util to the max(@rq, @p) effective uclamp values.
> - *
> - * If sched_uclamp_used static key is disabled, then just return the util
> - * without any clamping since uclamp aggregation at the rq level in the fast
> - * path is disabled, rendering this operation a NOP.
> - *
> - * Use uclamp_eff_value() if you don't care about uclamp values at rq level. It
> - * will return the correct effective uclamp value of the task even if the
> - * static key is disabled.
> - */
> -static __always_inline
> -unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> -                                 struct task_struct *p)
> -{
> -       unsigned long min_util = 0;
> -       unsigned long max_util = 0;
> -
> -       if (!static_branch_likely(&sched_uclamp_used))
> -               return util;
> -
> -       if (p) {
> -               min_util = uclamp_eff_value(p, UCLAMP_MIN);
> -               max_util = uclamp_eff_value(p, UCLAMP_MAX);
> -
> -               /*
> -                * Ignore last runnable task's max clamp, as this task will
> -                * reset it. Similarly, no need to read the rq's min clamp.
> -                */
> -               if (uclamp_rq_is_idle(rq))
> -                       goto out;
> -       }
> -
> -       min_util = max_t(unsigned long, min_util, uclamp_rq_get(rq, UCLAMP_MIN));
> -       max_util = max_t(unsigned long, max_util, uclamp_rq_get(rq, UCLAMP_MAX));
> -out:
> -       /*
> -        * Since CPU's {min,max}_util clamps are MAX aggregated considering
> -        * RUNNABLE tasks with _different_ clamps, we can end up with an
> -        * inversion. Fix it now when the clamps are applied.
> -        */
> -       if (unlikely(min_util >= max_util))
> -               return min_util;
> -
> -       return clamp(util, min_util, max_util);
> -}
> -
>  /* Is the rq being capped/throttled by uclamp_max? */
>  static inline bool uclamp_rq_is_capped(struct rq *rq)
>  {
> @@ -3148,13 +3095,6 @@ static inline unsigned long uclamp_eff_value(struct task_struct *p,
>         return SCHED_CAPACITY_SCALE;
>  }
>
> -static inline
> -unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> -                                 struct task_struct *p)
> -{
> -       return util;
> -}
> -
>  static inline bool uclamp_rq_is_capped(struct rq *rq) { return false; }
>
>  static inline bool uclamp_is_used(void)
> --
> 2.34.1
>