Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757392AbbLBXij (ORCPT ); Wed, 2 Dec 2015 18:38:39 -0500 Received: from mail-yk0-f174.google.com ([209.85.160.174]:36572 "EHLO mail-yk0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755306AbbLBXii (ORCPT ); Wed, 2 Dec 2015 18:38:38 -0500 MIME-Version: 1.0 In-Reply-To: References: <1A7043D5F58CCB44A599DFD55ED4C948469538F6@fmsmsx115.amr.corp.intel.com> Date: Wed, 2 Dec 2015 15:38:37 -0800 Message-ID: Subject: Re: Skylake (XPS 13 9350) TSC is way off From: John Stultz To: Andy Lutomirski Cc: "Brown, Len" , "linux-kernel@vger.kernel.org" , X86 ML , "Hunter, Adrian" 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: 1745 Lines: 45 On Wed, Dec 2, 2015 at 3:25 PM, Andy Lutomirski wrote: > In case it's at all useful, adjtimex -p says: > > mode: 0 > offset: 0 > frequency: 135641 > maxerror: 37498 > esterror: 1532 > status: 8192 > time_constant: 2 > precision: 1 > tolerance: 32768000 > tick: 10000 > raw time: 1449098317s 671243180us = 1449098317.671243180 > > this suggests a rather small correction, so I really have no idea what > "Adjusting tsc more than 11% (8039115 vs 7759462)" means. > > John, you wrote this code. What does the error message mean? Basally the internal correction adjustments are getting pulled further then it is supposed to (its concerning since in some cases we push the clocksource mult value to be quite large, and so making a large adjustment could possibly cause an overflow). Awhile back I had intended to cap the max adjustment, but out of caution I put in a warning instead to see how often this might occur. I've seen it reported sometimes while folks were running trinity or under a VM (suggesting that due to system delays timekeeping management may have been delayed and the internal time error had grown quite far, so the internal correction was being somewhat aggressive). Though more recently (3.17 era) we've changed the internal adjustment code to try to be more conservative to avoid over-steering w/ NOHZ, so I'd expect fewer of these. On a hunch, are you running chrony instead of ntpd? 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/