linux-kernel - Re: [PATCH v9 08/10] sched: replace capacity

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Message-ID: <20141124171635.GL23177@e105550-lin.cambridge.arm.com>
Date:	Mon, 24 Nov 2014 17:16:35 +0000
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"kamalesh@...ux.vnet.ibm.com" <kamalesh@...ux.vnet.ibm.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v9 08/10] sched: replace capacity_factor by usage

On Mon, Nov 24, 2014 at 02:41:28PM +0000, Vincent Guittot wrote:
> On 21 November 2014 at 13:37, Morten Rasmussen <morten.rasmussen@....com> wrote:
> > On Mon, Nov 03, 2014 at 04:54:45PM +0000, Vincent Guittot wrote:
> 
> [snip]
> 
> >>                  */
> >>                 if (prefer_sibling && sds->local &&
> >> -                   sds->local_stat.group_has_free_capacity)
> >> -                       sgs->group_capacity_factor = min(sgs->group_capacity_factor, 1U);
> >> +                   group_has_capacity(env, &sds->local_stat) &&
> >> +                   (sgs->sum_nr_running > 1)) {
> >> +                       sgs->group_no_capacity = 1;
> >> +                       sgs->group_type = group_overloaded;
> >> +               }
> >
> > I'm still a bit confused about SD_PREFER_SIBLING. What is the flag
> > supposed to do and why?
> 
> The goal is to spread tasks across the group even if the the latter is
> not overloaded. for SMT level, the goal is to have 1 task per core
> before 1 task per HW thread

That makes more sense and is in line with how I understand SMT
scheduling. So we try to have at least one task per group. Where each
group is a domain with SD_PREFER_SIBLING.

Anyway, you don't change the prefer-sibling behaviour in this patch set.
I was just wondering how it would work for SMT balancing.

Thanks,
Morten
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