From: Petri Kaukasoina <kaukasoina704m93hd7@sci.fi>
To: Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
Clark Williams <williams@redhat.com>,
zippel@linux-m68k.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] tsc_khz= boot option to avoid TSC calibration variance
Date: Wed, 13 May 2009 12:23:35 +0300 [thread overview]
Message-ID: <20090513092335.GA22832@elektroni.phys.tut.fi> (raw)
In-Reply-To: <4A0A9A23.24720.54D53C4@Ulrich.Windl.rkdvmks1.ngate.uni-regensburg.de>
On Wed, May 13, 2009 at 09:59:59AM +0200, Ulrich Windl wrote:
> On 13 May 2009 at 0:42, Thomas Gleixner wrote:
>
> > Honestly all this is just the futile attempt to fix the flaws of NTP
> > via (super)user interaction.
>
> This has nothing to do with flaws in NTP (AFAIK).
Correct. When ntp is NOT RUNNING at all, if the TSC calibration gives a MHz
value differing e.g. 100 ppm from the previous value, the clock will run at
a different speed, 100 ppm making a difference of 17 seconds a day. On the
other hand, if ntp is running, it will eventually compensate the offset. But
it takes quite a long time to settle, IMO too long for a quality time
server.
The real changes in the clock frequency between bootups are in the order of
1 ppm, but the TSC calibration can be even 100 ppm off randomly.
-Petri
next prev parent reply other threads:[~2009-05-13 9:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-12 2:12 john stultz
2009-05-12 8:36 ` Ulrich Windl
2009-05-12 22:26 ` john stultz
2009-05-12 22:42 ` Thomas Gleixner
2009-05-12 23:02 ` john stultz
2009-05-13 9:41 ` Petri Kaukasoina
2009-05-13 7:59 ` Ulrich Windl
2009-05-13 9:23 ` Petri Kaukasoina [this message]
2009-05-13 10:06 ` Petri Kaukasoina
2009-05-12 13:20 ` Serge Belyshev
2009-05-12 23:31 ` john stultz
2009-05-13 18:45 ` George Spelvin
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