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Date: Mon, 11 May 2009 18:13:13 -0700 From: john stultz <johnstul@...ibm.com> To: mingo@...hat.com, hpa@...or.com, riel@...hat.com, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...e.hu Cc: linux-tip-commits@...r.kernel.org, Bernhard Schiffner <bernhard@...iffner-limbach.de> Subject: Re: [tip:timers/ntp] ntp: adjust SHIFT_PLL to improve NTP convergence On Wed, 2009-05-06 at 09:46 +0000, tip-bot for john stultz wrote: > Commit-ID: 22cfbbfd9f67b67fe073010f51cb71d3632387d5 > Gitweb: http://git.kernel.org/tip/22cfbbfd9f67b67fe073010f51cb71d3632387d5 > Author: john stultz <johnstul@...ibm.com> > AuthorDate: Wed, 6 May 2009 11:43:57 +0200 > Committer: Ingo Molnar <mingo@...e.hu> > CommitDate: Wed, 6 May 2009 11:44:02 +0200 > > ntp: adjust SHIFT_PLL to improve NTP convergence > > The conversion to the ntpv4 reference model > f19923937321244e7dc334767eb4b67e0e3d5c74 ("ntp: convert to the NTP4 > reference model") in 2.6.19 added nanosecond resolution the adjtimex > interface, but also changed the "stiffness" of the frequency adjustments, > causing NTP convergence time to greatly increase. > > SHIFT_PLL, which reduces the stiffness of the freq adjustments, was > designed to be inversely linked to HZ, and the reference value of 4 was > designed for Unix systems using HZ=100. However Linux's clock steering > code mostly independent of HZ. > > So this patch reduces the SHIFT_PLL value from 4 to 2, which causes NTPd > behavior to match kernels prior to 2.6.19, greatly reducing convergence > times, and improving close synchronization through environmental thermal > changes. > > The patch also changes some l's to L's in nearby code to avoid misreading > 50l as 501. > > [ Impact: tweak NTP algorithm for faster convergence ] Bernhard Schiffner noticed I had a few comment typos in this patch, (note: to save embarrassment, when making typos, avoid copying and pasting them) so this patch corrects them. Signed-off-by: John Stultz <johnstul@...ibm.com> diff --git a/include/linux/timex.h b/include/linux/timex.h index 0daf961..9910e3b 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -179,7 +179,7 @@ struct timex { * NTP convergence time. A higher value makes it stiffer, increasing * convergence time, but making the clock more stable. * - * In David Mills' nanokenrel reference implmentation SHIFT_PLL is 4. + * In David Mills' nanokernel reference implementation SHIFT_PLL is 4. * However this seems to increase convergence time much too long. * * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html @@ -196,7 +196,7 @@ struct timex { * * SHIFT_FLL is used as a dampening factor to define how much we * adjust the frequency correction for a given offset in FLL mode. - * In David Mills' nanokenrel reference implmentation SHIFT_PLL is 2. + * In David Mills' nanokernel reference implementation SHIFT_FLL is 2. * * MAXTC establishes the maximum time constant of the PLL. */ -- 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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