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

From	Mike Galbraith <umgwanakikbuti@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [patch] sched: Fix smp nice induced group scheduling load distribution woes
Date	2016-04-28 14:30 +0200
Message-ID	<rsTeV-32p-11@gated-at.bofh.it> (permalink)
References	(1 earlier) <rrhbI-4rx-9@gated-at.bofh.it> <rrml4-A9-15@gated-at.bofh.it> <rrKQp-3ck-7@gated-at.bofh.it> <rsrVo-5zE-23@gated-at.bofh.it> <rsQh4-Jd-17@gated-at.bofh.it>
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On Thu, 2016-04-28 at 11:11 +0200, Peter Zijlstra wrote:
> 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) ?

Duh, nope.

> 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.

Yup, works, and you don't have to carefully blink as you skim past it.

> ---
> 
> 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)

Thread

[RFC] The Linux Scheduler: a Decade of Wasted Cores Report Jeff Merkey <linux.mdb@gmail.com> - 2016-04-23 20:30 +0200
  Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Brendan Gregg <brendan.d.gregg@gmail.com> - 2016-04-24 03:40 +0200
    Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-24 09:10 +0200
      Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-25 11:20 +0200
        [patch] sched: Fix smp nice induced group scheduling load  distribution woes Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-27 09:20 +0200
          Re: [patch] sched: Fix smp nice induced group scheduling load  distribution woes Peter Zijlstra <peterz@infradead.org> - 2016-04-28 11:20 +0200
            Re: [patch] sched: Fix smp nice induced group scheduling load  distribution woes Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-28 14:30 +0200
    Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Peter Zijlstra <peterz@infradead.org> - 2016-04-25 11:40 +0200
      Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Rik van Riel <riel@redhat.com> - 2016-04-25 20:00 +0200

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