linux-kernel - Re: [PATCH v5 11/12] sched: replace capacity

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Date:	Sun, 14 Sep 2014 21:51:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Rik van Riel <riel@...hat.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v5 11/12] sched: replace capacity_factor by utilization

On Sun, Sep 14, 2014 at 09:41:56PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 11, 2014 at 07:26:48PM +0200, Vincent Guittot wrote:
> > On 11 September 2014 18:15, Peter Zijlstra <peterz@...radead.org> wrote:
> > > On Tue, Aug 26, 2014 at 01:06:54PM +0200, Vincent Guittot wrote:
> > >> +static inline int group_has_free_capacity(struct sg_lb_stats *sgs,
> > >> +                     struct lb_env *env)
> > >>  {
> > >> +     if ((sgs->group_capacity_orig * 100) >
> > >> +                     (sgs->group_utilization * env->sd->imbalance_pct))
> > >> +             return 1;
> > >> +
> > >> +     if (sgs->sum_nr_running < sgs->group_weight)
> > >> +             return 1;
> > >>
> > >> +     return 0;
> > >> +}
> > >>
> > >> +static inline int group_is_overloaded(struct sg_lb_stats *sgs,
> > >> +                     struct lb_env *env)
> > >> +{
> > >> +     if (sgs->sum_nr_running <= sgs->group_weight)
> > >> +             return 0;
> > >>
> > >> +     if ((sgs->group_capacity_orig * 100) <
> > >> +                     (sgs->group_utilization * env->sd->imbalance_pct))
> > >> +             return 1;
> > >>
> > >> +     return 0;
> > >>  }
> > >
> > > I'm confused about the utilization vs capacity_orig. I see how we should
> > 
> > 1st point is that I should compare utilization vs capacity and not
> > capacity_orig.
> > I should have replaced capacity_orig by capacity in the functions
> > above when i move the utilization statistic from
> > rq->avg.runnable_avg_sum to cfs.usage_load_avg.
> > rq->avg.runnable_avg_sum was measuring all activity on the cpu whereas
> > cfs.usage_load_avg integrates only cfs tasks
> > 
> > With this change, we don't need sgs->group_capacity_orig anymore but
> > only sgs->group_capacity. So sgs->group_capacity_orig can be removed
> > as it's no more used in the code as sg_capacity_factor has been
> > removed
> 
> Yes, but.. so I suppose we need to add DVFS accounting and remove
> cpufreq from the capacity thing. Otherwise I don't see it make sense.

That is to say, please also explain these details in the changelog, and
preferably also in a XXX/FIXME/TODO comment near wherever so we don't
forget about it.
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