Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267527AbUIPHOY (ORCPT ); Thu, 16 Sep 2004 03:14:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267494AbUIPHOX (ORCPT ); Thu, 16 Sep 2004 03:14:23 -0400 Received: from rrzd2.rz.uni-regensburg.de ([132.199.1.12]:40900 "EHLO rrzd2.rz.uni-regensburg.de") by vger.kernel.org with ESMTP id S267545AbUIPHJX (ORCPT ); Thu, 16 Sep 2004 03:09:23 -0400 From: "Ulrich Windl" Organization: Universitaet Regensburg, Klinikum To: john stultz Date: Thu, 16 Sep 2004 09:02:03 +0200 MIME-Version: 1.0 Subject: Re: [RFC][PATCH] new timeofday core subsystem (v.A0) CC: george anzinger , Albert Cahalan , lkml , tim@physik3.uni-rostock.de, Ulrich.Windl@rz.uni-regensburg.de, Len Brown , linux@dominikbrodowski.de, David Mosberger , Andi Kleen , paulus@samba.org, schwidefsky@de.ibm.com, jimix@us.ibm.com, keith maanthey , greg kh , Patricia Gaughen , Chris McDermott Message-ID: <4149568C.32693.473C38@rkdvmks1.ngate.uni-regensburg.de> In-reply-to: <1095274131.29408.2990.camel@cog.beaverton.ibm.com> References: X-mailer: Pegasus Mail for Windows (4.21c) Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Content-description: Mail message body X-Content-Conformance: HerringScan-0.25/Sophos-3.84+2.20+2.07.066+02 August 2004+93426@20040916.065318Z Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1476 Lines: 29 On 15 Sep 2004 at 11:48, john stultz wrote: > NTP adjustments need to be applied smoothly and consistently as time > progresses. Adjustment to the NTP parameters occur at do_adjtimex and at Actually I think (constant) NTP adjustments need to be applied any time. That's why I even tried to correct the TSC interpolation between ticks (If you visit the PPSkit patch, that's the "nanoscale" thing). The "constant adjustment values" are updated regularly also (per tick, per second, per NTP update). The basic thought was: If the time between two ticks is not 1/HZ the TSC interpolation (that is calibrated against the timer ticks) also will not interpolate between 1/HZ ticks. I assumed the TSC interpolations is wrong by the same percentage the timer interrupts are. Thus I tried to reversely apply the frequency error learnt through NTP even to the TSC interpolation (in addition to the time increments every tick). My code however has the problem that I ran out of significant bits during several muliplies and divides, while supporting that maximum imaginable frequency range for TSC. Even with the best oscillator, it won't reach single nanosecond precision as I don't have enough bits for them. Regards, Ulrich - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/