linux-kernel - Re: [patch] sched: Fix smp nice induced group scheduling load distribution woes

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Message-ID: <20160428091152.GC3448@twins.programming.kicks-ass.net>
Date:	Thu, 28 Apr 2016 11:11:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Jeff Merkey <linux.mdb@...il.com>
Subject: Re: [patch] sched: Fix smp nice induced group scheduling load
 distribution woes

On Wed, Apr 27, 2016 at 09:09:51AM +0200, Mike Galbraith wrote:
> On even a modest sized NUMA box any load that wants to scale
> is essentially reduced to SCHED_IDLE class by smp nice scaling.
> Limit niceness to prevent cramming a box wide load into a too
> small space.  Given niceness affects latency, give the user the
> option to completely disable box wide group fairness as well.

Have you tried the (obvious) ?

I suppose we really should just do this (and yuyang's cleanup patches I
suppose). Nobody has ever been able to reproduce those increased power
usage claims and Google is running with this enabled.

---

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 69da6fcaa0e8..968f573413de 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -53,7 +53,7 @@ static inline void cpu_load_update_active(struct rq *this_rq) { }
  * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
  * increased costs.
  */
-#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load  */
+#ifdef CONFIG_64BIT
 # define SCHED_LOAD_RESOLUTION	10
 # define scale_load(w)		((w) << SCHED_LOAD_RESOLUTION)
 # define scale_load_down(w)	((w) >> SCHED_LOAD_RESOLUTION)