linux-kernel - Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG

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Message-Id: <20110531083859.98e4ff43.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 31 May 2011 08:38:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Christoph Lameter <cl@...ux.com>,
	Mel Gorman <mel@....ul.ie>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH] mm, vmstat: Use cond_resched only when !CONFIG_PREEMPT

On Mon, 30 May 2011 22:59:04 +0600
Rakib Mullick <rakib.mullick@...il.com> wrote:

> commit 468fd62ed9 (vmstats: add cond_resched() to refresh_cpu_vm_stats()) added cond_resched() in refresh_cpu_vm_stats. Purpose of that patch was to allow other threads to run in non-preemptive case. This patch, makes sure that cond_resched() gets called when !CONFIG_PREEMPT is set. In a preemptiable kernel we don't need to call cond_resched().
> 
> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>

Hmm, what benefit do we get by adding this extra #ifdef in the code directly ?
Other cond_resched() callers are not guilty in !CONFIG_PREEMPT ?

Thanks,
-Kame

> ---
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 20c18b7..72cf857 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -461,7 +461,11 @@ void refresh_cpu_vm_stats(int cpu)
>  				p->expire = 3;
>  #endif
>  			}
> +
> +#ifndef CONFIG_PREEMPT
>  		cond_resched();
> +#endif
> +
>  #ifdef CONFIG_NUMA
>  		/*
>  		 * Deal with draining the remote pageset of this
> 
> 

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