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To: Bruce Evans <bde@zeta.org.au>
cc: freebsd-current@freefall.freebsd.org, kuku@gilberto.physik.rwth-aachen.de
Subject: Re: calcru: negative time: 
In-reply-to: Your message of "Mon, 01 Apr 1996 21:15:40 +1000."
             <199604011115.VAA15805@godzilla.zeta.org.au> 
From: David Greenman <davidg@Root.COM>
Reply-To: davidg@Root.COM
Date: Mon, 01 Apr 1996 13:51:31 -0800
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>>[deleted]
>>calcru: negative time: -11929 usec
>>calcru: negative time: -3909 usec
>>calcru: negative time: -3842 usec
>>calcru: negative time: -17709 usec
>>calcru: negative time: -3480 usec
>
>This is caused by hardclock() interrupt latency.  The problem is
>especially noticable on i586's and i686's because any latency causes the
>clock to go backwards; on i386's and i486's, the latency must be > 1
>clock tick (10000 usec) to cause problems.  Normally the latency on
>i586's is > 0 but < 10 usec and isn't detectable.  There must be bugs
>elsewhere to cause latencies of more than a few tens of usecs.

   I'm not convinced that this is a latency problem. The problem has suddenly
gotten about 1000 times worse earlier today on both -current and -stable
simultaneously...and it's not due to any code changes or load changes. I saw
the problem on machines ranging from wcarchive to my X terminal (which is
a FreeBSD machine). Note also that as of right now the problem seems to have
disappeared again. This looks to me like a strange bug related to the date/
time of year (that it coincides with April Fools Day, has got to be the most
amazing thing of all).

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project