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

[Vincent Guittot]

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.
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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