linux-kernel - Re: [PATCH] sched: remove redundant check in select_task_rq

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Message-ID: <1307440414.2322.236.camel@twins>
Date:	Tue, 07 Jun 2011 11:53:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: remove redundant check in select_task_rq_fair

On Tue, 2011-06-07 at 15:18 +0530, Nikunj A. Dadhania wrote:
> When balancing for wakeup affinity, a redundant check can removed.

Yes, tempting, but no, now you've got an extra call to wake_affine(),
which is more expensive.

> Signed-off-by: Nikunj A. Dadhania <nikunj@...ux.vnet.ibm.com>
> ---
>  kernel/sched_fair.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 433491c..b9e5701 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1753,7 +1753,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>  	}
>  
>  	if (affine_sd) {
> -		if (cpu == prev_cpu || wake_affine(affine_sd, p, sync))
> +		if (wake_affine(affine_sd, p, sync))
>  			prev_cpu = cpu;
>  
>  		new_cpu = select_idle_sibling(p, prev_cpu);
> 

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