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Date: Thu, 24 Mar 2011 17:19:28 -0600
From: Warner Losh <imp@bsdimp.com>
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Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org, Peter Jeremy <peterjeremy@acm.org>,
	Jung-uk Kim <jkim@FreeBSD.org>
Subject: Re: svn commit: r219700 - head/sys/x86/x86
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On 03/23/2011 06:34, John Baldwin wrote:
> On Thursday, March 17, 2011 5:06:09 pm Jung-uk Kim wrote:
>> On Thursday 17 March 2011 04:01 pm, Peter Jeremy wrote:
>>> On 2011-Mar-16 16:44:08 +0000, Jung-uk Kim<jkim@FreeBSD.org>  wrote:
>>>> Log:
>>>>   Revert r219676.
>>> Thanks also.  For extra kudos, how about adding a similar function
>>> to allow the HPET frequency to be over-ridden.  That is currently
>>> the only timecounter that does not allow the user to compensate for
>>> incorrect hardware frequencies.
>> I really hate the idea of adjusting timecounter frequency from
>> userland.  I guess "use ntpd(8)" is not a good answer for some
>> people. :-(
> Actually, that doesn't work well if your timecounter frequency is off by a
> lot.  Having the timecounter frequency accurate improves the accuracy of
> things like ntpd and ptpd.

ntpd requires that the time counter be within 128ppm of true.  If the 
time counter guess is off by more than that, you lose: ntpd won't work.

Warner