linux-kernel - [tip:sched/urgent] sched: Ensure update_cfs_shares() is called for parents of continuously-running tasks

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Date:	Wed, 31 Jul 2013 01:55:28 -0700
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	pjt@...gle.com, peterz@...radead.org, max@...tavus.edu,
	stable@...nel.org, tglx@...utronix.de
Subject: [tip:sched/urgent] sched: Ensure update_cfs_shares()
  is called for parents of continuously-running tasks

Commit-ID:  bf0bd948d1682e3996adc093b43021ed391983e6
Gitweb:     http://git.kernel.org/tip/bf0bd948d1682e3996adc093b43021ed391983e6
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 26 Jul 2013 23:48:42 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 30 Jul 2013 22:14:37 +0200

sched: Ensure update_cfs_shares() is called for parents of continuously-running tasks

We typically update a task_group's shares within the dequeue/enqueue
path.  However, continuously running tasks sharing a CPU are not
subject to these updates as they are only put/picked.  Unfortunately,
when we reverted f269ae046 (in 17bc14b7), we lost the augmenting
periodic update that was supposed to account for this; resulting in a
potential loss of fairness.

To fix this, re-introduce the explicit update in
update_cfs_rq_blocked_load() [called via entity_tick()].

Reported-by: Max Hailperin <max@...tavus.edu>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Reviewed-by: Paul Turner <pjt@...gle.com>
Link: http://lkml.kernel.org/n/tip-9545m3apw5d93ubyrotrj31y@git.kernel.org
Cc: <stable@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 98d1355..06db94b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2032,6 +2032,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 	 */
 	update_entity_load_avg(curr, 1);
 	update_cfs_rq_blocked_load(cfs_rq, 1);
+	update_cfs_shares(cfs_rq);
 
 #ifdef CONFIG_SCHED_HRTICK
 	/*
--
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