From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A996C433E1 for ; Mon, 18 May 2020 11:26:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5679320709 for ; Mon, 18 May 2020 11:26:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726958AbgERL0R convert rfc822-to-8bit (ORCPT ); Mon, 18 May 2020 07:26:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726585AbgERL0R (ORCPT ); Mon, 18 May 2020 07:26:17 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 388E4C061A0C for ; Mon, 18 May 2020 04:26:17 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jaduR-0008K2-H1; Mon, 18 May 2020 13:26:15 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 03E0E100606; Mon, 18 May 2020 13:26:14 +0200 (CEST) From: Thomas Gleixner To: Pali =?utf-8?Q?Roh=C3=A1r?= Cc: linux-kernel@vger.kernel.org Subject: Re: Missing CLOCK_BOOTTIME_RAW? In-Reply-To: <20200518111103.sj73h5j3r75zv2wp@pali> References: <20200508213122.f7srcd2gnduamtvs@pali> <87zhah4evs.fsf@nanos.tec.linutronix.de> <20200518111103.sj73h5j3r75zv2wp@pali> Date: Mon, 18 May 2020 13:26:14 +0200 Message-ID: <87ftbxxz55.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Pali Rohár writes: > On Saturday 09 May 2020 11:49:27 Thomas Gleixner wrote: >> Sure, but what's the problem? The adjustemt is done to make the observed >> time as correct as possible. > > Yes. But correction may take lot of time, e.g. also more then one day. > > So during this period when correction is in progress, measuring time > difference via CLOCK_MONITONIC will have incorrect results. > > It already happened for me, system clock was shifted by one hour and > chronyd started adjustment, it slow down system clock. 6 real hours > passed and via system clock was measured time difference only about > 5 hours and 20 minutes (correction was still in progress as system > clock at that time was still shifted by about 20 minutes). System clock shifted by one hour? You mean DST change? If chronyd adjusts that by smoothing the frequency, that's just broken and really not the kernel's problem. Thanks, tglx