linux-kernel - Re: [PATCH] sched: Accelerate "pick_next

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Message-ID: <1326707503.2442.219.camel@twins>
Date:	Mon, 16 Jan 2012 10:51:43 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Accelerate "pick_next_entity" under special
 condition

On Mon, 2012-01-16 at 17:37 +0800, Michael Wang wrote:
> From: Michael Wang <wangyun@...ux.vnet.ibm.com>
> 
> We can avoid some useless operation in some special condition.

This is a pretty empty statement.

> For example:
> If we have "cfs_rq->next" and it can be use, we just return it directly.

What it doesn't state is what it actually does, if it affects the common
case and performance numbers (or a good reason for the lack thereof).

> Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>
> ---
>  kernel/sched/fair.c |   28 +++++++++++++++++-----------
>  1 files changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 84adb2d..9fc2c3c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1295,6 +1295,8 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  static int
>  wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
>  
> +#define ENTITY_PREEMPT_ALLOWED(prev,next)	(wakeup_preempt_entity(prev, next) < 1)

This is just uglification imo, its shouting and it doesn't actually win
you much space.

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