linux-kernel - Re: [PATCH v4 08/12] sched: move cfs task on a CPU with higher capacity

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Message-ID: <53D699BE.90208@redhat.com>
Date:	Mon, 28 Jul 2014 14:43:10 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>, peterz@...radead.org,
	mingo@...nel.org, linux-kernel@...r.kernel.org,
	preeti@...ux.vnet.ibm.com, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org
CC:	Morten.Rasmussen@....com, efault@....de, nicolas.pitre@...aro.org,
	linaro-kernel@...ts.linaro.org, daniel.lezcano@...aro.org,
	dietmar.eggemann@....com
Subject: Re: [PATCH v4 08/12] sched: move cfs task on a CPU with higher capacity

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On 07/28/2014 01:51 PM, Vincent Guittot wrote:
> If the CPU is used for handling lot of IRQs, trig a load balance to
> check if it's worth moving its tasks on another CPU that has more
> capacity.
> 
> As a sidenote, this will note generate more spurious ilb because we
> already trig an ilb if there is more than 1 busy cpu. If this cpu
> is the only one that has a task, we will trig the ilb once for
> migrating the task.
> 
> The nohz_kick_needed function has been cleaned up a bit while
> adding the new test
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org> --- 
> kernel/sched/fair.c | 69
> +++++++++++++++++++++++++++++++++++++---------------- 1 file
> changed, 49 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index
> 6843016..1cde8dd 100644 --- a/kernel/sched/fair.c +++
> b/kernel/sched/fair.c @@ -5969,6 +5969,14 @@ static bool
> update_sd_pick_busiest(struct lb_env *env, return true; }
> 
> +	/* +	 * The group capacity is reduced probably because of
> activity from other +	 * sched class or interrupts which use part
> of the available capacity +	 */ +	if ((sg->sgc->capacity_orig *
> 100) > (sgs->group_capacity * +				env->sd->imbalance_pct)) +
> return true; + return false; }

Isn't this already reflected in avg_load, by having avg_load increase
due to the capacity decreasing when a cpu is busy with non-CFS loads?

Also, this part of update_sd_pick_busiest will not be reached in the
!SD_ASYM_PACKING case once my patch is applied, so this is a small
conflict between our series :)

- -- 
All rights reversed
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