From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751981AbaIYGHx (ORCPT ); Thu, 25 Sep 2014 02:07:53 -0400 Received: from mail-wi0-f177.google.com ([209.85.212.177]:58405 "EHLO mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750793AbaIYGHv (ORCPT ); Thu, 25 Sep 2014 02:07:51 -0400 Date: Thu, 25 Sep 2014 07:07:45 +0100 From: Sitsofe Wheeler To: Olaf Hering Cc: Thomas Shao , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, driverdev-devel@linuxdriverproject.org, apw@canonical.com, jasowang@redhat.com, kys@microsoft.com, haiyangz@microsoft.com Subject: Re: [PATCH] Drivers: hv: util: Implement Time Synchronization using host time sample Message-ID: <20140925060745.GA9450@sucs.org> References: <1411451081-13423-1-git-send-email-huishao@microsoft.com> <20140923075610.GA10933@aepfle.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140923075610.GA10933@aepfle.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 23, 2014 at 09:56:10AM +0200, Olaf Hering wrote: > On Tue, Sep 23, Thomas Shao wrote: > > > In current hyper-v time sync service,it only gets the initial clock time > > from the host. It didn't process the following time samples. This change > > introduced a module parameter called host_time_sync. If it is set to true, > > the guest will periodically sychronize it's time with the host clock using > > host time sample. By default it is disabled, because we still recommend > > user to configure NTP for time synchronization. You [Microsoft?] do? Can you link to public sources where is this stated please? I don't see any mention of doing this on http://technet.microsoft.com/en-us/library/dn720239.aspx .. The only official Microsoft information with respect to Hyper-V guest time synchronisation I've seen has been for Windows guests but perhaps I've looked in the wrong places. The reason I ask is because regular ntpd is not enough to discipline a Linux Hyper-V guest's clock. So much drift can occur under load that ntpd can't bring the clock under sync. For now, I've been using Chrony which has a higher tolerance for correcting drifting clocks. I'm not the only one seeing this either (see http://serverfault.com/a/488528/203726 and http://serverfault.com/questions/523389/linux-clock-loses-10-minutes-every-week ). It would be good to something official about this issue as it is painful when happens. -- Sitsofe | http://sucs.org/~sits/