linux-kernel - Re: [PATCH 07/14] sched: agressively pack at wake/fork/exec

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Date:	Fri, 26 Apr 2013 15:08:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, mingo@...nel.org,
	linux@....linux.org.uk, pjt@...gle.com, santosh.shilimkar@...com,
	Morten.Rasmussen@....com, chander.kashyap@...aro.org,
	cmetcalf@...era.com, tony.luck@...el.com, alex.shi@...el.com,
	preeti@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net, l.majewski@...sung.com
Subject: Re: [PATCH 07/14] sched: agressively pack at wake/fork/exec

On Thu, Apr 25, 2013 at 07:23:23PM +0200, Vincent Guittot wrote:
> According to the packing policy, the scheduler can pack tasks at different
> step:
> -SCHED_PACKING_NONE level: we don't pack any task.
> -SCHED_PACKING_DEFAULT: we only pack small tasks at wake up when system is not
> busy.
> -SCHED_PACKING_FULL: we pack tasks at wake up until a CPU becomes full. During
> a fork or a exec, we assume that the new task is a full running one and we
> look for an idle CPU close to the buddy CPU.

This changelog is very short on explaining how it will go about achieving these
goals.

> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/fair.c |   47 ++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 98166aa..874f330 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3259,13 +3259,16 @@ static struct sched_group *
>  find_idlest_group(struct sched_domain *sd, struct task_struct *p,


So for packing into power domains, wouldn't you typically pick the busiest non-
full domain to fill from other non-full?

Picking the idlest non-full seems like it would generate a ping-pong or not
actually pack anything.
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