From: "George Spelvin" <linux@horizon.com>
To: johnstul@us.ibm.com
Cc: linux-kernel@vger.kernel.org, linux@horizon.com,
tglx@linutronix.de, ulrich.windl@rz.uni-regensburg.de,
williams@redhat.com, zippel@linux-m68k.org
Subject: Re: [RFC][PATCH] Adjust SHIFT_PLL to improve NTP convergence.
Date: 6 May 2009 10:46:45 -0400 [thread overview]
Message-ID: <20090506144645.30215.qmail@science.horizon.com> (raw)
In-Reply-To: <1241471016.7444.80.camel@localhost.localdomain>
> As always, feedback or testing (especially on non-x86 arches) would be
> greatly appreciated.
Applying it to a couple of PPS-synchronized machines (where I had already
dropped the poll interval into the basement for better convergence, have
to try reverting that) seems to be working.
One thing I just noticed, although I'm sure it has happened in the past,
is that there's a frequency jump each boot due to TSC recalibration.
Machine 1 Machine 2
Old CPU MHz 2500.170 2500.138
Old NTP ppm -24.63 +/-0.01 -30.27 +/-0.02
New CPU MHz 2500.176 2500.193
New NTP ppm -22.26 +/-0.01 -8.20 +/-0.015
"True" CPU MHz 2500.2316 2500.2136
I should look and see if there's an easy way to tighten that tolerance.
The current algorithm is fine for jiffies purposes, but a few seconds'
worth of background calibration would produce a more stable estimate.
next prev parent reply other threads:[~2009-05-06 14:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-04 21:03 john stultz
2009-05-05 0:27 ` Rik van Riel
2009-05-06 14:46 ` George Spelvin [this message]
2009-05-06 15:44 ` John Stultz
2009-05-07 6:07 ` George Spelvin
2009-05-07 9:14 ` Ulrich Windl
2009-05-07 18:07 ` George Spelvin
2009-05-07 19:37 ` john stultz
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