Re: [PATCH v7 6/7] sched: replace capacity_factor by usage

[Wanpeng Li]

Hi Vincent,
On 10/9/14, 10:18 PM, Vincent Guittot wrote:
> On 9 October 2014 14:16, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Tue, Oct 07, 2014 at 02:13:36PM +0200, Vincent Guittot wrote:
> > > +static inline bool
> > > +group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
> > >   {
> > > +     if ((sgs->group_capacity * 100) >
> > > +                     (sgs->group_usage * env->sd->imbalance_pct))
> > > +             return true;
> > Why the imb_pct there? We're looking for 100% utilization, not 130 or
> > whatnot, right?
> Having exactly 100% is quite difficult because of various rounding.

Could you give some examples about the various roundingï

Regards,
Wanpeng Li

> So i have added a margin/threshold to prevent any excessive change of the state.
> I have just to use the same margin/threshold than in other place in
> load balance.
>
> so the current threshold depends of the sched_level. it's around 14% at MC level
>
> > > +     if (sgs->sum_nr_running < sgs->group_weight)
> > > +             return true;
> > With the code as it stands, this is the cheaper test (no mults) so why
> > is it second?
> >
> > > +     return false;
> > > +}
> > >
> > > +static inline bool
> > > +group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
> > > +{
> > > +     if (sgs->sum_nr_running <= sgs->group_weight)
> > > +             return false;
> > > +
> > > +     if ((sgs->group_capacity * 100) <
> > > +                     (sgs->group_usage * env->sd->imbalance_pct))
> > > +             return true;
> > >
> > > +     return false;
> > >   }
> > Same thing here wrt imb_pct
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