Re: [PATCH v5 11/12] sched: replace capacity_factor by utilization

[Dietmar Eggemann]

On 14/09/14 12:41, 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@xxxxxxxxxxxxx> 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.

My understanding is that uArch scaling of capacacity_orig (therefore of 
capacity too) is done by calling arch_scale_cpu_capacity and frequency 
scaling for capacity is done by calling arch_scale_freq_capacity in 
update_cpu_capacity. I understand that this patch-set does not provide 
an implementation of arch_scale_freq_capacity though.

The uArch and frequency scaling of load & utilization will be added 
later. I know that Morten is currently working on a 'uArch and frequency 
invariant load & utilization tracking' patch-set.

Although I don't know exactly what you mean by DVFS accounting and 
remove cpufreq from the capacity here.

-- Dietmar

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