linux-kernel - Re: [PATCH 1/2] sched/fair: Fix how load gets propagated from cfs_rq to its sched

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Date:   Tue, 2 May 2017 10:30:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
        Chris Mason <clm@...com>, kernel-team@...com
Subject: Re: [PATCH 1/2] sched/fair: Fix how load gets propagated from cfs_rq
 to its sched_entity

On Tue, May 02, 2017 at 10:19:05AM +0200, Peter Zijlstra wrote:
> Can you have a play with something like the below? I suspect
> 'shares_runnable' might work for you here.

> ---
>  kernel/sched/fair.c | 62 +++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 44 insertions(+), 18 deletions(-)

So something like so on top I suppose...

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3101,38 +3101,7 @@ static inline void
 update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	struct cfs_rq *gcfs_rq = group_cfs_rq(se);
-	long delta, load = gcfs_rq->avg.load_avg;
-
-	/*
-	 * If the load of group cfs_rq is null, the load of the
-	 * sched_entity will also be null so we can skip the formula
-	 */
-	if (load) {
-		long tg_load;
-
-		/* Get tg's load and ensure tg_load > 0 */
-		tg_load = atomic_long_read(&gcfs_rq->tg->load_avg) + 1;
-
-		/* Ensure tg_load >= load and updated with current load*/
-		tg_load -= gcfs_rq->tg_load_avg_contrib;
-		tg_load += load;
-
-		/*
-		 * We need to compute a correction term in the case that the
-		 * task group is consuming more CPU than a task of equal
-		 * weight. A task with a weight equals to tg->shares will have
-		 * a load less or equal to scale_load_down(tg->shares).
-		 * Similarly, the sched_entities that represent the task group
-		 * at parent level, can't have a load higher than
-		 * scale_load_down(tg->shares). And the Sum of sched_entities'
-		 * load must be <= scale_load_down(tg->shares).
-		 */
-		if (tg_load > scale_load_down(gcfs_rq->tg->shares)) {
-			/* scale gcfs_rq's load into tg's shares*/
-			load *= scale_load_down(gcfs_rq->tg->shares);
-			load /= tg_load;
-		}
-	}
+	long delta, load = calc_cfs_shares(gcfs_rq, gcfs_rq->tg, shares_runnable);
 
 	delta = load - se->avg.load_avg;