Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932436AbbLHBOk (ORCPT ); Mon, 7 Dec 2015 20:14:40 -0500 Received: from mail-qk0-f180.google.com ([209.85.220.180]:33155 "EHLO mail-qk0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932207AbbLHBOj (ORCPT ); Mon, 7 Dec 2015 20:14:39 -0500 MIME-Version: 1.0 In-Reply-To: <20151207144319.GB1402@localhost> References: <1449266274-26517-1-git-send-email-john.stultz@linaro.org> <20151207144319.GB1402@localhost> Date: Mon, 7 Dec 2015 17:14:38 -0800 Message-ID: Subject: Re: [RFC][PATCH] timekeeping: Cap adjustments so they don't exceede the maxadj value From: John Stultz To: Miroslav Lichvar Cc: lkml , Thomas Gleixner , Richard Cochran , Prarit Bhargava , Andy Lutomirski Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1479 Lines: 36 On Mon, Dec 7, 2015 at 6:43 AM, Miroslav Lichvar wrote: > On Fri, Dec 04, 2015 at 01:57:54PM -0800, John Stultz wrote: >> Thus its been occasionally noted that users have seen >> confusing warnings like: >> >> Adjusting tsc more than 11% (5941981 vs 7759439) > > Thanks for looking into this, John. > >> Thus this patch adds some extra logic to enforce the max adjustment >> cap in the internal steering. >> >> Note: This has the potential to slow corrections when the ADJ_TICK >> value is furthest away from the default value. So it would be good to >> get some testing from folks using Chrony, to make sure we don't >> cause any troubles there. > > I ran few tests with chronyd, forcing it to make the largest possible > adjustment of the tick and it seems to work fine. > > However, I'm still able to trigger the warning by feeding a large > offset to the NTP PLL using a short time constant. When the multiplier > is already at the maximum and it wants to move it even further, there > should be no timekeeping_apply_adjustment() call as it always adjusts > the multiplier at least by one. Ack. Thanks for noticing this. I could reproduce it and have a fix. Will send an update out later. thanks -john -- 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/