linux-kernel - Re: [PATCH v7 6/7] sched: replace capacity

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Message-ID: <CAKfTPtCX687FkGgxLO7spfGvDxhDWeFDERLRZ-NakO2Jrpmnhw@mail.gmail.com>
Date:	Thu, 9 Oct 2014 16:18:02 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Kamalesh Babulal <kamalesh@...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>,
	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>,
	Paul Turner <pjt@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>
Subject: Re: [PATCH v7 6/7] sched: replace capacity_factor by usage

On 9 October 2014 14:16, Peter Zijlstra <peterz@...radead.org> 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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