linux-kernel - Re: [PATCH v2 11/11] sched: replace capacity by activity

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Date:	Thu, 29 May 2014 21:56:24 +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>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....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>
Subject: Re: [PATCH v2 11/11] sched: replace capacity by activity

On 29 May 2014 16:02, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, May 23, 2014 at 05:53:05PM +0200, Vincent Guittot wrote:
>> @@ -6052,8 +6006,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>>                * with a large weight task outweighs the tasks on the system).
>>                */
>>               if (prefer_sibling && sds->local &&
>> -                 sds->local_stat.group_has_capacity)
>> -                     sgs->group_capacity = min(sgs->group_capacity, 1U);
>> +                 sds->local_stat.group_capacity > 0)
>> +                     sgs->group_capacity = min(sgs->group_capacity, 1L);
>>
>>               if (update_sd_pick_busiest(env, sds, sg, sgs)) {
>>                       sds->busiest = sg;
>> @@ -6228,7 +6182,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>>                * have to drop below capacity to reach cpu-load equilibrium.
>>                */
>>               load_above_capacity =
>> -                     (busiest->sum_nr_running - busiest->group_capacity);
>> +                     (busiest->sum_nr_running - busiest->group_weight);
>>
>>               load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_POWER_SCALE);
>>               load_above_capacity /= busiest->group_power;
>
> I think you just broke PREFER_SIBLING here..

you mean by replacing the capacity which was reflecting the number of
core for SMT by the group_weight ?

>
> So we want PREFER_SIBLING to work on nr_running, not utilization because
> we want to spread single tasks around, regardless of their utilization.
>
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