linux-kernel - Re: [PATCH 2/4] sched/fair: Remove SCHED_LOAD_SHIFT and SCHED_LOAD

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Date:	Tue, 6 Oct 2015 11:29:27 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH 2/4] sched/fair: Remove SCHED_LOAD_SHIFT and SCHED_LOAD_SCALE

On 4 October 2015 at 19:56, Yuyang Du <yuyang.du@...el.com> wrote:
> After cleaning up the sched metrics, these two definitions that cause
> ambiguity are not needed any more. Use NICE_0_LOAD_SHIFT and NICE_0_LOAD
> instead (the names suggest clearly who they are).
>
> Suggested-by: Ben Segall <bsegall@...gle.com>
> Signed-off-by: Yuyang Du <yuyang.du@...el.com>
> ---
>  kernel/sched/fair.c  |  4 ++--
>  kernel/sched/sched.h | 22 +++++++++++-----------
>  2 files changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c61fd8e..fdb7937 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -682,7 +682,7 @@ void init_entity_runnable_average(struct sched_entity *se)
>         sa->period_contrib = 1023;
>         sa->load_avg = scale_load_down(se->load.weight);
>         sa->load_sum = sa->load_avg * LOAD_AVG_MAX;
> -       sa->util_avg = scale_load_down(SCHED_LOAD_SCALE);
> +       sa->util_avg = SCHED_CAPACITY_SCALE;
>         sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
>         /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
>  }
> @@ -6651,7 +6651,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>         if (busiest->group_type == group_overloaded &&
>             local->group_type   == group_overloaded) {
>                 load_above_capacity = busiest->sum_nr_running *
> -                                       SCHED_LOAD_SCALE;
> +                                       SCHED_CAPACITY_SCALE;

load_above_capacity is then compared against load_avg. In patch 3, you
directly use weight instead of scale_down(weight) to compute the
load_avg. It implies that load_above_capacity must also move to the
same range. So you will have to replace SCHED_CAPACITY_SCALE with
NICE_0_LOAD.
This comment applied to patch 3 but it was easier to describe the
issue here with the code than doing that in patch 3 which doesn't have
reference to this code

So you should better use scale_down(NICE_0_LOAD) in this patch and
remove the scale_down in patch 3 to keep only NICE_0_LOAD so you will
be consistent in each patch


>                 if (load_above_capacity > busiest->group_capacity)
>                         load_above_capacity -= busiest->group_capacity;

Here you will also have to move the capacity in the same range than
the load. So in patch 3 you will have to use
scale_load(busiest->group_capacity)

Regards,
Vincent

>                 else
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 31b4022..3d03956 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -53,25 +53,25 @@ static inline void update_cpu_load_active(struct rq *this_rq) { }
>   * increased costs.
>   */
>  #if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load  */
> -# define SCHED_LOAD_SHIFT      (SCHED_RESOLUTION_SHIFT + SCHED_RESOLUTION_SHIFT)
> +# define NICE_0_LOAD_SHIFT     (SCHED_RESOLUTION_SHIFT + SCHED_RESOLUTION_SHIFT)
>  # define scale_load(w)         ((w) << SCHED_RESOLUTION_SHIFT)
>  # define scale_load_down(w)    ((w) >> SCHED_RESOLUTION_SHIFT)
>  #else
> -# define SCHED_LOAD_SHIFT      (SCHED_RESOLUTION_SHIFT)
> +# define NICE_0_LOAD_SHIFT     (SCHED_RESOLUTION_SHIFT)
>  # define scale_load(w)         (w)
>  # define scale_load_down(w)    (w)
>  #endif
>
> -#define SCHED_LOAD_SCALE       (1L << SCHED_LOAD_SHIFT)
> -
>  /*
> - * NICE_0's weight (visible to user) and its load (invisible to user) have
> - * independent resolution, but they should be well calibrated. We use scale_load()
> - * and scale_load_down(w) to convert between them, the following must be true:
> - * scale_load(prio_to_weight[20]) == NICE_0_LOAD
> + * Task weight (visible to user) and its load (invisible to user) have
> + * independent resolution, but they should be well calibrated. We use
> + * scale_load() and scale_load_down(w) to convert between them. The
> + * following must be true:
> + *
> + *  scale_load(prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]) == NICE_0_LOAD
> + *
>   */
> -#define NICE_0_LOAD            SCHED_LOAD_SCALE
> -#define NICE_0_SHIFT           SCHED_LOAD_SHIFT
> +#define NICE_0_LOAD            (1L << NICE_0_LOAD_SHIFT)
>
>  /*
>   * Single value that decides SCHED_DEADLINE internal math precision.
> @@ -850,7 +850,7 @@ DECLARE_PER_CPU(struct sched_domain *, sd_asym);
>  struct sched_group_capacity {
>         atomic_t ref;
>         /*
> -        * CPU capacity of this group, SCHED_LOAD_SCALE being max capacity
> +        * CPU capacity of this group, SCHED_CAPACITY_SCALE being max capacity
>          * for a single CPU.
>          */
>         unsigned int capacity;
> --
> 2.1.4
>
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