linux-kernel - Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average tracking

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Date:	Mon, 28 Jul 2014 12:48:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org, pjt@...gle.com,
	bsegall@...gle.com, arjan.van.de.ven@...el.com,
	len.brown@...el.com, rafael.j.wysocki@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, fengguang.wu@...el.com
Subject: Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average
 tracking

On Fri, Jul 18, 2014 at 07:26:06AM +0800, Yuyang Du wrote:
> @@ -665,20 +660,27 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  }
>  
>  #ifdef CONFIG_SMP
> -static unsigned long task_h_load(struct task_struct *p);
>  
> -static inline void __update_task_entity_contrib(struct sched_entity *se);
> +/* dependent on LOAD_AVG_PERIOD, see below */
> +#define LOAD_AVG_MAX 47742 /* maximum possible load avg */

Please don't separate this from the rest of the values it belongs to. If
you really have to, move the entire block.

> @@ -2071,13 +2073,9 @@ static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
>  	long tg_weight;
>  
>  	/*
> -	 * Use this CPU's actual weight instead of the last load_contribution
> -	 * to gain a more accurate current total weight. See
> -	 * update_cfs_rq_load_contribution().
> +	 * Use this CPU's load average instead of actual weight
>  	 */
>  	tg_weight = atomic_long_read(&tg->load_avg);
> -	tg_weight -= cfs_rq->tg_load_contrib;
> -	tg_weight += cfs_rq->load.weight;

I don't think that comment makes any sense after this. The comment was
there to explain the -=, += things, but that's all gone so its pretty
trivial now, and i++ /* inc by one */ comments are not useful.

> @@ -2181,7 +2178,7 @@ static const u32 runnable_avg_yN_sum[] = {
>   * Approximate:
>   *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
>   */
> -static __always_inline u64 decay_load(u64 val, u64 n)
> +static __always_inline u64 decay_load32(u64 val, u64 n)
>  {
>  	unsigned int local_n;
>  
> @@ -2210,6 +2207,18 @@ static __always_inline u64 decay_load(u64 val, u64 n)
>  	return val >> 32;
>  }
>  
> +static __always_inline u64 decay_load(u64 val, u64 n)
> +{
> +	if (likely(val <= UINT_MAX))
> +		val = decay_load32(val, n);
> +	else {
> +		val *= (u32)decay_load32(1 << 15, n);
> +		val >>= 15;
> +	}
> +
> +	return val;
> +}

Please just use mul_u64_u32_shr().

/me continues reading the rest of it..

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