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Date: Wed, 20 Feb 2002 08:50:32 -0800
From: george anzinger <george@mvista.com>
Organization: Monta Vista Software
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To: Bill Davidsen <davidsen@tmr.com>
CC: Ben Greear <greearb@candelatech.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: jiffies rollover, uptime etc.
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Bill Davidsen wrote:
> 
> On Tue, 19 Feb 2002, george anzinger wrote:
> 
> > Bill Davidsen wrote:
> > >
> > > On Mon, 18 Feb 2002, Ben Greear wrote:
> 
> > > > Does this problem still exist on 64-bit machines?
> > >
> > > Absolutely. But not as often ;-)
> >
> > Actually you will have a VERY hard time getting it to roll over.  Issues
> > of your life time, not to mention the hardware's life time.  64 bits
> > makes a VERY large number and you are counting in 427 day increments.
> > Remember we have been counting seconds since 1970 in 32 bits and
> > rollover is still, most likely, beyond the capability of any machine
> > running today to get to.  Now consider counting in 427 day increments
> > instead of seconds.
> 
> Um, note the odd characters appended to my sentence ";-)" which means
> "not serious here, look for joke, sarcasm, over or understatement.
> 
Ok, I guess I just got so impressed with the size of a 64-bit value that
I was overwhelmed.  Consider, for example:

	u64 i;
	for (i = 1; i != 0; i++);

Now in theory this will count each possible number, but in practice the
machine will die long before it ever finishes.
	
-- 
George           george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Real time sched: http://sourceforge.net/projects/rtsched/
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