From owner-freebsd-current  Tue Jul 14 20:30:53 1998
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	Wed, 15 Jul 1998 13:30:29 +1000
Date: Wed, 15 Jul 1998 13:30:29 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199807150330.NAA22646@godzilla.zeta.org.au>
To: jak@cetlink.net
Subject: Re: tickadj -t not changing tick
Sender: owner-freebsd-current@FreeBSD.ORG
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X-Loop: FreeBSD.ORG

>Has anyone else noticed that tickadj -t is broken in -current?  It
>does not change the tick.

I think it changes the kernel `tick' variable.  However, this variable
is not used for timekeeping in -current.  It is only used to calculate
timeout intervals.

>I can tell by setting the tick to a very low or high value like 9951
>or 10049, and then running ntpdate -b every few minutes to see if the
>time step function of ntpdate is compensating for the low/high tick
>value.  In 2.2.5 it does, but in -current it does not.

`tick' shouldn't be changed in any version of 2.2 or -current.  Instead,
change some of the the lower-level timer variables machdep.i586_freq,
machdep.tsc_freq and machdep.i8254_freq using sysctl to make `tick'
actually correct.  These variables should be set correctly enough by
default, just like `tick', but if not, changing them works better than
changing `tick' because the change routines propagate necessary changes
to associated variables and/or hardware programming.

The relevant sysctl variables depend on the the FreeBSD version and
configuration:

machdep.i8254_freq: always exists, never hurts to set it right, but only
	essential for it to be right on systems using it for timekeeping
	(2.2., -current on sub-586's and 586+'s running SMP or APM.
machdep.i586_freq: 2.2 name for machdep.tsc_freq.  Doesn't hurt to set it
	right, but not essential for it it be right.
machdep.tsc_freq: -current only, must be right if it is used for timekeeping.
	It is used on 586+'s not running SMP or APM.

Bruce

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