linux-kernel - Re: [PATCH 2/3] sched: Use clamp() and clamp

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Message-ID: <20140305102658.4c7ffe2c@gandalf.local.home>
Date:	Wed, 5 Mar 2014 10:26:58 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Dongsheng Yang <yangds.fnst@...fujitsu.com>,
	linux-kernel@...r.kernel.org, fweisbec@...il.com,
	peterz@...radead.org, mingo@...hat.com,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 2/3] sched: Use clamp() and clamp_val() to make it more
 readable.

On Wed, 05 Mar 2014 07:17:36 -0800
Joe Perches <joe@...ches.com> wrote:

> On Wed, 2014-03-05 at 20:36 +0800, Dongsheng Yang wrote:
> > As Kees suggested, I use clamp() function to replace the if and
> > else branch, making it more readable and modular.
> > 
> > Suggested-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: Dongsheng Yang <yangds.fnst@...fujitsu.com>
> []
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> []
> > @@ -3070,17 +3070,10 @@ SYSCALL_DEFINE1(nice, int, increment)
> >  	 * We don't have to worry. Conceptually one call occurs first
> >  	 * and we have a single winner.
> >  	 */
> > -	if (increment < -40)
> > -		increment = -40;
> > -	if (increment > 40)
> > -		increment = 40;
> > -
> > +	increment = clamp(increment, -40, 40);
> 
> Maybe:
> 
> 	increment = clamp(increment, -(NICE_MAX - NICE_MIN + 1), 
> 				   , NICE_MAX - NICE_MIN + 1)

Ug, that's much harder to read.

> 
> or add yet another define like #define NICE_RANGE
> or #define NICE_MAX_INCREMENT

Sure, if there's a NICE_MAX_INC == 40, then we could do:

	increment = clamp(increment, -NICE_MAX_INC, NICE_MAX_INC);

-- Steve
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