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 15:42:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Jirka Hladky <jhladky@...hat.com>,
	linux-kernel <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>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Matt Fleming <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 02:44:07PM +0200, Vincent Guittot wrote:
> > --- 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;
> 
> IIUC, you are reverting
> commit  fde7d22e01aa (sched/fair: Fix overly small weight for
> interactive group entities)

Hurm.. looking at that commit again, that seems to wreck
effective_load(), since that doesn't compensate.

Maybe I'll remove calc_tg_weight and open code its slightly different
usages in the two sites.