Date: Sun, 27 Apr 1997 22:30:47 +1000 From: Bruce Evans <bde@zeta.org.au> To: cvs-all@FreeBSD.org, CVS-committers@FreeBSD.org, cvs-etc@FreeBSD.org, jkh@FreeBSD.org Subject: Re: cvs commit: src/etc rc rc.network Message-ID: <199704271230.WAA07923@godzilla.zeta.org.au>
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> Branch: etc RELENG_2_2
> Modified: etc rc rc.network
> Log:
> tickadj is useful even if ntpdate isn't selected (clock drift isn't
> isolated to network time users) so make it a fully independant knob.
> Suggested-By: Richard Crook <richard@sj.co.uk>
tickadj is not useful:
BUGS
Fiddling with kernel variables at run time as a part of
ordinary operations is a hideous practice which is only
necessary to make up for deficiencies in the implementa-
tion of adjtime(8) in many kernels and/or brokenness of
^ bug, should be 2
the system clock in some vendors' kernels. It would be
much better if the kernels were fixed and the tickadj pro-
gram went away.
Since FreeBSD's adjtime(2) doesn't have these deficiencies, there is no
need for tickadj.
In FreeBSD-2.2, you can also fine tune the system clock using `sysctl
-w machdep.i8254_freq=whatever'. This sets the nominal frequency to
match the actual frequency (the actual frequency can be inferred from
the drift). It has much the same effect as using tickadj to modify
`tick' except it is free from certain undesirable side effects of
modifying `tick'. Resolution is limited to +-0.5 usec per tick for
the same reasons as it is limited for the tickadj method (this will
be fixed someday), so you still need to use adjtime(8) or xntpd(8)
for fine control. adjtime(8) isn't standard in FreeBSD. I recommend
using xntpd with the kernel PLL even on systems not connected to networks.
In-FreeBSD-2.2, you can also use the option CLK_USE_I8254_CALIBRATION
to attempt to initialize the nominal i8254 frequency better, or you
can boot with -v and note the frequency and set it later using sysctl.
The frequency is calibrated relative to the RTC which may be more
accurate.
Bruce
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