linux-kernel - Re: 4.3 group scheduling regression

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Date:	Tue, 13 Oct 2015 03:32:47 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: 4.3 group scheduling regression

On Mon, Oct 12, 2015 at 01:47:23PM +0200, Peter Zijlstra wrote:
> 
> Also, should we do the below? At this point se->on_rq is still 0 so
> reweight_entity() will not update (dequeue/enqueue) the accounting, but
> we'll have just accounted the 'old' load.weight.
> 
> Doing it this way around we'll first update the weight and then account
> it, which seems more accurate.
 
I think the original looks ok.

The account_entity_enqueue() adds child entity's load.weight to parent's load:

update_load_add(&cfs_rq->load, se->load.weight)

Then recalculate the shares.

Then reweight_entity() resets the parent entity's load.weight.

> ---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 700eb548315f..d2efef565aed 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3009,8 +3009,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	 */
>  	update_curr(cfs_rq);
>  	enqueue_entity_load_avg(cfs_rq, se);
> -	account_entity_enqueue(cfs_rq, se);
>  	update_cfs_shares(cfs_rq);
> +	account_entity_enqueue(cfs_rq, se);
>  
>  	if (flags & ENQUEUE_WAKEUP) {
>  		place_entity(cfs_rq, se, 0);
--
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