From: Con Kolivas <kernel@kolivas.org>
To: "lk" <linux_kernel@patni.com>
Subject: Re: something about jiffies wraparound overflow
Date: Tue, 27 Dec 2005 20:05:21 +1100
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Cc: "jeff shia" <tshxiayu@gmail.com>, linux-kernel@vger.kernel.org,
       "robert love" <rml@novell.com>
References: <7cd5d4b40512262046w6f7a8161jfaf1e618e5722b4@mail.gmail.com> <003201c60ac3$16692d90$5e91a8c0@patni.com>
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On Tuesday 27 December 2005 19:54, lk wrote:
> As you mentioned the code for comparison:
> > /* code 2*/
> > unsigned long timeout = jiffies + HZ/2;
>
> the code has no problem with jiffies wrapping around
> as long as the values are compared in a right way.
> For a 32 bit platform the counter wraps around only once every 50 day
> when the value of HZ 1000. so if your code is prepared to face this event
> it will work fine.

In 2.6 we actually roll over 5 minutes after starting (the jiffy counter is 
set to about 5 minutes from roll over); that was put in on purpose to pick up 
wraparound bugs easily.

Cheers,
Con
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