From owner-freebsd-hackers  Wed Apr  7 12:55:42 1999
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Date: Wed, 7 Apr 1999 21:53:14 +0200
From: Eivind Eklund <eivind@freebsd.org>
To: Nick Sayer <nsayer@quack.kfu.com>
Cc: hackers@freebsd.org
Subject: Re: cvs commit: src/sys/kern kern_time.c
Message-ID: <19990407215314.B75317@bitbox.follo.net>
References: <199904071924.MAA05436@apollo.backplane.com> <199904071932.MAA38634@medusa.kfu.com>
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In-Reply-To: <199904071932.MAA38634@medusa.kfu.com>; from Nick Sayer on Wed, Apr 07, 1999 at 12:32:51PM -0700
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[Moved to -hackers]

On Wed, Apr 07, 1999 at 12:32:51PM -0700, Nick Sayer wrote:
> > :On Apr 7,  9:36am, Nick Sayer wrote:
> > :} Subject: cvs commit: src/sys/kern kern_time.c
> > :
> > :}   We still need to decide on an algorithm to clamp positive adjustments.
> > :}   As it stands, it is possible to achieve arbitrary negative adjustments
> > :}   by "wrapping" time around.
> > :
> > :Limit positive steps to MIN(1 second, elapsed time since last postive step).
> > :At worst the clock could be made to run at 2x normal speed.
> 
> I was looking at a much uglier version of the above, involving
> having a 'step allowed' variable that gets cleared by the clock
> interrupt or something, but the above looks much nicer. Let me
> go to my little workshop. :-)

I'd suggest going for at least a minute instead of a second, to allow
re-adjustement after loosing an ntp server for a while.  Possibly
more; I've not thought too closely about this.  It might be reasonable
to do

maxstep = MIN(1 minute, elapsed time since last positive step / 10)

to keep the present "max 10% time adjustement" limitation.

Eivind.


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