Date: Wed, 13 Jan 1999 16:52:03 +0900 From: Kenjiro Cho <kjc@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? Message-ID: <199901130752.QAA22585@hotaka.csl.sony.co.jp> In-Reply-To: Your message of "12 Jan 1999 22:31:56 %2B0100." <xzpzp7ob2k3.fsf@flood.ping.uio.no>
next in thread | previous in thread | raw e-mail | index | archive | help
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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199901130752.QAA22585>