linux-kernel - Re: [PATCH] sched: update blocked load of idle cpus

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Date:	Wed, 24 Jun 2015 07:41:14 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	peterz@...radead.org, pjt@...gle.com, bsegall@...gle.com,
	morten.rasmussen@....com, dietmar.eggemann@....com,
	len.brown@...el.com, rafael.j.wysocki@...el.com,
	fengguang.wu@...el.com, boqun.feng@...il.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: [PATCH] sched: update blocked load of idle cpus

Hi Vincent,

On Wed, Jun 24, 2015 at 09:11:12AM +0200, Vincent Guittot wrote:
> The load and the util of idle cpus must be updated periodically in order to
> decay the blocked part.
> 
> If CONFIG_FAIR_GROUP_SCHED is not set, the load and util of idle cpus
> are not decayed and stay at the values set before becoming idle.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> Hi Yuyang,
> 
> While testing your patchset without CONFIG_FAIR_GROUP_SCHED, i have noticed
> that the load of idle cpus stays sometimes to an high value whereas they were
> not used for a while because we are not decaying the blocked load.
> Futhermore, the peridodic load balance was not pulling tasks onto some idle
> cpus because their load stayed high.
> 
> This patchset fixes the issue. 

Thanks. We should privide an update_blocked_averages() for the
CONFIG_FAIR_GROUP_SCHED=n case. Great.

> 
> Regards,
> Vincent
> 
>  kernel/sched/fair.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c5f18d9..665cc4b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5864,6 +5864,17 @@ static unsigned long task_h_load(struct task_struct *p)
>  #else
>  static inline void update_blocked_averages(int cpu)
>  {
> +	struct rq *rq = cpu_rq(cpu);
> +	struct cfs_rq *cfs_rq = &rq->cfs;
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&rq->lock, flags);
> +	update_rq_clock(rq);
> +
> +	update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq))
> +
> +	raw_spin_unlock_irqrestore(&rq->lock, flags);
> +
>  }
>  
>  static unsigned long task_h_load(struct task_struct *p)

Reviewed-by: Yuyang Du <yuyang.du@...el.com>

> -- 
> 1.9.1
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