linux-kernel - Re: [PATCH] sched: deduplicate mm checks in normalize_rt

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Message-ID: <20110421132904.GA2702@zhy>
Date:	Thu, 21 Apr 2011 21:29:04 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] sched: deduplicate mm checks in normalize_rt_tasks()

On Thu, Apr 21, 2011 at 09:15:56PM +0800, Hillf Danton wrote:
> When normalizing realtime tasks, only user tasks are concerned by
> checking their ->mm.
> If the task is not realtime, the -mm is checked again, thus the
> overwork could be removed.
> 
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> ---
> 
> --- a/kernel/sched.c	2011-03-30 03:09:48.000000000 +0800
> +++ b/kernel/sched.c	2011-04-21 20:59:28.000000000 +0800
> @@ -8364,7 +8364,7 @@ void normalize_rt_tasks(void)
>  			 * Renice negative nice level userspace
>  			 * tasks back to 0:
>  			 */
> -			if (TASK_NICE(p) < 0 && p->mm)
> +			if (TASK_NICE(p) < 0)

This looks good.

And we can also move TASK_NICE(p) < 0 to the upper if(),
like:
		if (!rt_task(p) && TASK_NICE(p) < 0) {
			set_user_nice(p, 0);
			continue;
		}

to reduce one level if() to make code cleaner :)

Thanks,
Yong

>  				set_user_nice(p, 0);
>  			continue;
>  		}
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