From owner-freebsd-current  Tue Jan 12 23:53:00 1999
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id XAA18205
          for freebsd-current-outgoing; Tue, 12 Jan 1999 23:53:00 -0800 (PST)
          (envelope-from owner-freebsd-current@FreeBSD.ORG)
Received: from widefw.csl.sony.co.jp (widefw.csl.sony.co.jp [133.138.1.1])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id XAA18151
          for <current@FreeBSD.ORG>; Tue, 12 Jan 1999 23:52:45 -0800 (PST)
          (envelope-from kjc@csl.sony.co.jp)
Received: from hotaka.csl.sony.co.jp (root@hotaka.csl.sony.co.jp [43.27.98.57])
	by widefw.csl.sony.co.jp (8.8.8/3.6W) with ESMTP id QAA08053;
	Wed, 13 Jan 1999 16:52:04 +0900 (JST)
Received: from localhost (kjc@[127.0.0.1])
	by hotaka.csl.sony.co.jp (8.8.8/3.6W/hotaka/98122515) with ESMTP id QAA22585;
	Wed, 13 Jan 1999 16:52:03 +0900 (JST)
Message-Id: <199901130752.QAA22585@hotaka.csl.sony.co.jp>
To: Dag-Erling Smorgrav <des@flood.ping.uio.no>, Bruce Evans <bde@zeta.org.au>
cc: current@FreeBSD.ORG
Subject: Re: HZ missing in options? 
In-reply-to: Your message of "12 Jan 1999 22:31:56 +0100."
             <xzpzp7ob2k3.fsf@flood.ping.uio.no> 
Date: Wed, 13 Jan 1999 16:52:03 +0900
From: Kenjiro Cho <kjc@csl.sony.co.jp>
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG


Dag-Erling Smorgrav <des@flood.ping.uio.no> said:
  > Kenjiro Cho <kjc@csl.sony.co.jp> writes:
  > Is there any reason why HZ isn't listed in sys/conf/options?
  > Or just an oversight?  If so, I'll add the following line.

>> Perhaps because it's not a user-tunable option? or is it?

The 4.4BSD has the following lines in conf/param.c and HZ has been a
config option.

/*
 * System parameter formulae.
 *
 * This file is copied into each directory where we compile
 * the kernel; it should be modified there to suit local taste
 * if necessary.
 *
 * Compiled with -DHZ=xx -DTIMEZONE=x -DDST=x -DMAXUSERS=xx
 */

In FreeBSD-2.1, -DHZ=xx was removed when TIMEZONE and DST were
eliminated.

Bruce Evans <bde@zeta.org.au> said:
>> Changing it used to break xntpd's kernel PLL.  Increasing it used to
>> significantly increase the potential inaccuracy of the clock (from
>> 50 ppm for 100 Hz to 500 ppm for 1000 Hz).  Increasing it is still
>> harmful for adjtime(2).  This shouldn't be a problem except when xntpd
>> is misconfigured to use adjtime() instead of the kernel PLL.

As I understand it,
 - the impact to adjtime(2) is that, when HZ > 500, the clock can be
   adjusted more than 30ms in 60sec (1usec adjust/tick).
 - xnpd (when properly configured) uses ntp_adjtime(2) instead of 
   adjtime(2) and it has no problem with a higher resolution.

Am I missing any other issues?

--Kenjiro

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message