Date: Fri, 25 Dec 2009 09:35:04 +0100
From: Arjan van de Ven <arjan@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Smith, GeoffX" <geoffx.smith@intel.com>, Andi Kleen <andi@firstfloor.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Michael Stone <michael@laptop.org>
Subject: Re: [PATCH] prctl: return MCE process flags through pointer
Message-ID: <20091225093504.0c1224a2@infradead.org>
In-Reply-To: <20091223105450.8f15db9f.akpm@linux-foundation.org>
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On Wed, 23 Dec 2009 10:54:50 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> 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?  

the largest I've seen asked in practice is 2 seconds.
But even at 100 msec or more you're talking about very special
applications; rounding up timers otherwise really impacts the
functionality of the app in a bad way.


> If so, what is it, and if so, why this:
> 
> #define MAX_SLACK       (100 * NSEC_PER_MSEC)

this is the max for "automatic slack"

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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