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

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Date:	Sun, 23 Nov 2014 09:03:16 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>,
	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

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？

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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