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

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Date:	Mon, 24 Nov 2014 11:16:09 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 23 November 2014 at 02:03, Wanpeng Li <kernellwp@...il.com> wrote:
> Hi Vincent,
> On 10/9/14, 10:18 PM, Vincent Guittot wrote:
>>
>> 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.
>
>
> Could you give some examples about the various rounding？

As an example while I was monitoring the runnable_load_sum and the
runnable_load_period, they were varying a bit around the max value but
was not always the same which can change the load_avg_contrib by few
unit

Regards,
Vincent

>
> 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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