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Date:      Wed, 21 Jul 1999 08:27:13 +0200 (SAT)
From:      John Hay <>
To: (David Schwartz)
Cc:        stable@FreeBSD.ORG
Subject:   Re: Tuning the system's clock
Message-ID:  <>
In-Reply-To: <000001bed2fc$593b6990$> from David Schwartz at "Jul 20, 1999 03:08:08 pm"

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> 	FreeBSD's internal high-precision clock seems to be based on the
> processor's instruction cycle counter. I've found that on one machine, the
> clock is about 150 ppm fast. So I tried to reduce the machdep.tsc_freq
> value. That was bad -- instant reboot.
> 	Is there a better way of adjusting that value? Changing 'tick' doesn't seem
> to do much.

I use it (machdep.tsc_freq and machdep.i8254_freq) here a lot and haven't
seen any problems... except on machines like SMP boxes that don't use the
tsc. There is does cause a panic. Bruce did fix it in current a few days
ago, but I don't think it has filtered down to stable yet.

> 	Are the NTP pll values for mult/div documented anywhere? It seems to divide
> before it multiplies, which means that using them for small offsets would
> require high divisors, and hence a loss of accuracy.

No it isn't documented anywhere AFAIK. Poul-Henning Kamp experimented
with it a while back, but I'm not even sure he is using it anymore.
It can probably be removed.

John Hay --

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