*BSD News Article 65412


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From: mday@elbereth.org (Matt Day)
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.advocacy,comp.os.linux.misc
Subject: Re: Linux or FreeBSD, which is more reliable?
Date: 4 Apr 1996 23:51:25 -0700
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Message-ID: <4k2ftd$f7c@coyote.Artisoft.COM>
References: <4jt34a$1nm@news7.erols.com> <4jugkl$fun@cebaf4.cebaf.gov>
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In article <4jugkl$fun@cebaf4.cebaf.gov> doolitt@recycle.cebaf.gov (Larry Doolittle) writes:
>Linux can only be expected to stay up 248 days, at which time the
>100Hz jiffy counter will go negative.  Solutions are:
> 1. Slow down the clock
> 2. Run on an alpha (1024 Hz and 64-bit jiffies)
> 3. Initialize jiffies to 214748000048 and debug what happens after an hour
> 4. Add the line 
>/sbin/shutdown -r +705600 "running out of jiffies"
>    to your /etc/rc.d/rc.local  (thanks, Werner)

The jiffies counter (in both Linux 1.2.13 and 1.3.76) is an unsigned
long, so it can't go negative.  This means it should be good for at
least 497 days, not 248.

I took a cursory glance at the timer-list code (kernel/sched.c) in
Linux 1.3.76 and it looks to me like it will indeed break when the
jiffies counter rolls over.  Could someone more familiar with the code
verify this?  It looks to me like the fix would be non-trivial.

Matt Day <mday@elbereth.org>