From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756730AbdABTmh (ORCPT ); Mon, 2 Jan 2017 14:42:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43986 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933995AbdABTlR (ORCPT ); Mon, 2 Jan 2017 14:41:17 -0500 From: Vitaly Kuznetsov To: devel@linuxdriverproject.org Cc: linux-kernel@vger.kernel.org, "K. Y. Srinivasan" , Haiyang Zhang , John Stultz , Thomas Gleixner , Alex Ng Subject: [PATCH 0/4] hv_util: adjust system time smoothly Date: Mon, 2 Jan 2017 20:41:10 +0100 Message-Id: <20170102194114.657-1-vkuznets@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 02 Jan 2017 19:41:18 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (First, I have to admit I'm not a timekeeping expert ...) With TimeSync version 4 protocol support we started updating system time continuously through the whole lifetime of Hyper-V guests. Every 5 seconds there is a time sample from the host which triggers do_settimeofday[64](). While the time from the host is very accurate such adjustments may cause issues: - Time is jumping forward and backward, some applications may misbehave. - In case an NTP client is run in parallel things may go south, e.g. when an NTP client tries to adjust tick/frequency with ADJ_TICK/ADJ_FREQUENCY the Hyper-V module will not see this changes and time will oscillate and never converge. - Systemd starts annoying you by printing "Time has been changed" every 5 seconds to the system log. With this series I suggest to use do_adjtimex() to adjust time. My tests show that such method gives equally good time convergence but avoids all the drawbacks described above. Vitaly Kuznetsov (4): timekeeping: export do_adjtimex() to modules hv_util: switch to using timespec64 hv_util: use do_adjtimex() to update system time hv_util: improve time adjustment accuracy by disabling interrupts drivers/hv/hv_util.c | 33 +++++++++++++++++++++++++++++---- kernel/time/timekeeping.c | 1 + 2 files changed, 30 insertions(+), 4 deletions(-) -- 2.9.3