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Message-ID: <20090506144645.30215.qmail@science.horizon.com> Date: 6 May 2009 10:46:45 -0400 From: "George Spelvin" <linux@...izon.com> To: johnstul@...ibm.com Cc: linux-kernel@...r.kernel.org, linux@...izon.com, tglx@...utronix.de, ulrich.windl@...uni-regensburg.de, williams@...hat.com, zippel@...ux-m68k.org Subject: Re: [RFC][PATCH] Adjust SHIFT_PLL to improve NTP convergence. > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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