linux-kernel - Re: [PATCH v1 01/10] sched/fair: Chance LOAD_AVG_MAX

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Message-ID: <CAKfTPtCzx-F=ZKz7QBiiKWmEUOG-Fgyn4HdCE0WK89=+-c9ndw@mail.gmail.com>
Date:   Wed, 24 Aug 2016 18:01:32 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Yuyang Du <yuyang.du@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCH v1 01/10] sched/fair: Chance LOAD_AVG_MAX_N from 345 to 347

On 10 August 2016 at 02:14, Yuyang Du <yuyang.du@...el.com> wrote:
> In commit 5b51f2f80b3b906ce59bd4dce6eca3c7f34cb1b9
> Author: Paul Turner <pjt@...gle.com>
> Date:   Thu Oct 4 13:18:32 2012 +0200
>
>     sched: Make __update_entity_runnable_avg() fast
>
> Paul has a program to compute LOAD_AVG_MAX_N, which basically means
> how many periods (at least) are needed for LOAD_AVG_MAX, and the result
> of calc_conv(1024) is 345:
>
>   long mult_inv(long c, int n) {
>         return (c * runnable_avg_yN_inv[n]) >>  WMULT_SHIFT;
>   }
>
>   void calc_conv(long n) {
>         long old_n;
>         int i = -1;
>
>         printf("convergence (LOAD_AVG_MAX, LOAD_AVG_MAX_N)\n");
>         do {
>                 old_n = n;
>                 n = mult_inv(n, 1) + 1024;
>                 i++;
>         } while (n != old_n);
>         printf("%d> %ld\n", i - 1, n);
>         printf("\n");
>   }
>
> The initial value of i is -1, which should be 1 as far as I can tell.
> Accordingly, the final result of LOAD_AVG_MAX_N should be changed
> from 345 to 347.
>
> Signed-off-by: Yuyang Du <yuyang.du@...el.com>
> ---
>  kernel/sched/fair.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 4088eed..997297b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -666,7 +666,7 @@ static unsigned long task_h_load(struct task_struct *p);
>   */
>  #define LOAD_AVG_PERIOD 32
>  #define LOAD_AVG_MAX 47742 /* maximum possible load avg */
> -#define LOAD_AVG_MAX_N 345 /* number of full periods to produce LOAD_AVG_MAX */
> +#define LOAD_AVG_MAX_N 347 /* number of full periods to produce LOAD_AVG_MAX */

Acked-by: Vincent Guittot <vincent.guitto@...ar.org>

>
>  /* Give new sched_entity start runnable values to heavy its load in infant time */
>  void init_entity_runnable_average(struct sched_entity *se)
> --
> 1.7.9.5
>