linux-kernel - [tip:sched/core] sched/fair: Fix overly small weight for interactive group entities

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Message-ID: <tip-fde7d22e01aa0d252fc5c95fa11f0dac35a4dd59@git.kernel.org>
Date:	Tue, 20 Oct 2015 02:31:02 -0700
From:	tip-bot for Yuyang Du <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, peterz@...radead.org, linux-kernel@...r.kernel.org,
	dietmar.eggemann@....com, tglx@...utronix.de, mingo@...nel.org,
	torvalds@...ux-foundation.org, umgwanakikbuti@...il.com,
	yuyang.du@...el.com, efault@....de
Subject: [tip:sched/core] sched/fair:
  Fix overly small weight for interactive group entities

Commit-ID:  fde7d22e01aa0d252fc5c95fa11f0dac35a4dd59
Gitweb:     http://git.kernel.org/tip/fde7d22e01aa0d252fc5c95fa11f0dac35a4dd59
Author:     Yuyang Du <yuyang.du@...el.com>
AuthorDate: Tue, 13 Oct 2015 09:18:22 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 20 Oct 2015 10:13:34 +0200

sched/fair: Fix overly small weight for interactive group entities

Commit:

  9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")

led to an overly small weight for interactive group entities. The bad case
can be easily reproduced when a number of CPU hogs compete for the CPUs
at the same time (thanks to Mike). This is largly because the task group's
load average tracking cross CPUs lags behind the real changes.

To fix this we accelerate the group share distribution process by using
the load.weight of the cfs_rq. This may increase the entire group's
share, but we have to do so to protect the (fragile) interactive
tasks, especially from CPU hogs.

Reported-by: Mike Galbraith <umgwanakikbuti@...il.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>
Tested-by: Mike Galbraith <umgwanakikbuti@...il.com>
Signed-off-by: Yuyang Du <yuyang.du@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1444699103-20272-1-git-send-email-yuyang.du@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e2e348..bc62c50 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2363,7 +2363,7 @@ static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
 	 */
 	tg_weight = atomic_long_read(&tg->load_avg);
 	tg_weight -= cfs_rq->tg_load_avg_contrib;
-	tg_weight += cfs_rq_load_avg(cfs_rq);
+	tg_weight += cfs_rq->load.weight;
 
 	return tg_weight;
 }
@@ -2373,7 +2373,7 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
 	long tg_weight, load, shares;
 
 	tg_weight = calc_tg_weight(tg, cfs_rq);
-	load = cfs_rq_load_avg(cfs_rq);
+	load = cfs_rq->load.weight;
 
 	shares = (tg->shares * load);
 	if (tg_weight)
--
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