linux-kernel - Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and SPECjvm2008 benchmarks against 4.6 kernel

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Date:	Fri, 24 Jun 2016 14:02:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jirka Hladky <jhladky@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Kamil Kolakowski <kkolakow@...hat.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Yuyang Du <yuyang.du@...el.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	umgwanakikbuti@...il.com, bsegall@...gle.com, pjt@...gle.com,
	matt@...eblueprint.co.uk
Subject: Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and
 SPECjvm2008 benchmarks against 4.6 kernel

On Fri, Jun 24, 2016 at 09:44:41AM +0200, Jirka Hladky wrote:
> Hi Peter,
> 
> thanks a lot for looking into it!
> 
> I have tried to disable autogroups
> 
> sysctl -w kernel.sched_autogroup_enabled=0
> 
> and I can confirm that performance is then back at level as in 4.6 kernel.

So unless the heat has made me do really silly things, the below seems
to cure things. Could you please verify?


---
 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 22d64b3f5876..d4f6fb2f3057 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2484,7 +2484,7 @@ 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.weight;
+	tg_weight += cfs_rq->avg.load_avg;
 
 	return tg_weight;
 }
@@ -2494,7 +2494,7 @@ 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.weight;
+	load = cfs_rq->avg.load_avg;
 
 	shares = (tg->shares * load);
 	if (tg_weight)