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Date: Wed, 23 Dec 2009 10:54:50 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: "Smith, GeoffX" <geoffx.smith@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Michael Stone <michael@laptop.org>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH] prctl: return MCE process flags through pointer
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On Wed, 23 Dec 2009 09:56:04 -0800 "Smith, GeoffX" <geoffx.smith@intel.com> wrote:

> >Why are task_struct.timer_slack_ns and
> >task_struct.default_timer_slack_ns unsigned long, btw?  AFACIT we could
> >make them unsigned ints.
> 
> Timer slack is not a Boolean or enum, and we want the greatest range possible.  (Actually, I'd like to talk Arjan into using the same time structure as select(), but that's another discussion.) Internally hrtimer uses unsigned long.  I know long and unsigned long are the same on some architectures, but let's not introduce an unnatural restriction -- recall that arg2 is unsigned long.

Using unsigned ints will reduce the size of the task_struct.

Is there any conceivable case for a timer_slack which exceeds four
seconds?  If so, what is it, and if so, why this:

#define MAX_SLACK       (100 * NSEC_PER_MSEC)

?