Date: Wed, 27 Dec 1995 09:47:32 -0500 From: Gene Stark <gene@starkhome.cs.sunysb.edu> To: peter@haywire.dialix.com (Peter Wemm) Cc: current@freebsd.org Subject: Re: Tick, tock, adjust the clock Message-ID: <199512271447.JAA16464@starkhome.cs.sunysb.edu> In-Reply-To: peter@haywire.dialix.com's message of 27 Dec 1995 11:08:52 %2B0800 References: <199512261708.LAA14134@miller.cs.uwm.edu> <4bqic1$e6g@starkhome.cs.sunysb.edu>
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>>These step adjustments are extremley annoying to programs that run >>and clock things in the 10ms range. The clock jumps forward and >>backward like a jumping bean. If I discontinue running xntpd my >>time adjustment problems go away, but then my clock doesn't keep >>correct time. > >>Any ideas or fixes? Any good starting places to start hacking away to fix >>this? > >I've had the same problem for quite some time.. On all the >FreeBSD machines I have access to, the xntpd oscilates very very badly >(like you've shown) and eventually logs "not logging any more time >steps" or something like that. I solved this problem (on 486 systems) by using tickadj to adjust the value of "tick" a few notches off of its standard value of 10000. The values I had to use were obtained by trial and error, and are different on each system. For example, I recall having to use values like 9994 instead of 10000. I also use a driftfile to avoid the lengthy resync period when the system is rebooted. Changing the tick value causes the system time to increment at a different rate. This gets the drift rate of the clock into a region where xntpd can sync to it with slew adjustments rather than step adjustments. I still have a nagging suspicion that there is a problem with the timekeeping code, since on forty-some systems I never had to use a tick value above 10000, only below. This suggests systematic bias, probably in software. However at one point Bruce Evans assured me that he believed the stuff was working correctly, so I haven't investigated further. - Gene Stark
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