Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754392AbaJUITM (ORCPT ); Tue, 21 Oct 2014 04:19:12 -0400 Received: from www.linutronix.de ([62.245.132.108]:57492 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751192AbaJUITJ (ORCPT ); Tue, 21 Oct 2014 04:19:09 -0400 Date: Tue, 21 Oct 2014 10:19:06 +0200 (CEST) From: Thomas Gleixner To: Thomas Shao cc: "gregkh@linuxfoundation.org" , LKML , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "jasowang@redhat.com" , KY Srinivasan , John Stultz , Richard Cochran Subject: RE: [PATCH v2 1/2] timekeeping: add EXPORT_SYMBOL_GPL for do_adjtimex() In-Reply-To: Message-ID: References: <1413362372-16236-1-git-send-email-huishao@microsoft.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 21 Oct 2014, Thomas Shao wrote: > > I still do not have a consistent argument from you WHY you need to abuse > > do_adjtimex() to do that host - guest synchronization in the first place. > > > > I need a function to gradually slew guest time. do_adjtimex() provides all the > functionality. Also I could not find any other exposed func to do this. I'd like to > hear any feedback from you for this. As Richard and others told you already, there are various options: 1) Use NTP on that private network, which does not involve any kernel changes at all. Your argument, that this is hard for IT-Admins to set up is just ridiculous. If an IT-Admin is not able to set that up, then he should better stay away from setting up a guest in the first place, really. 2) As pointed out already by others PPS/PTP might be a proper solution for this. All it takes is a pair of timestamps (host/guest) injected into the proper subsystem and a controlling daemon on the guest side. That would also avoid the problem of running NTPd and your kernel side poor mans NTPd at the same time. That pseudo NTP thing is just hilarious, really. You take the host time stamp in timesync_onchannelcallback() and schedule work. From the work queue you correlate the host time stamp to the current time of the guest. So you correlate time stamps which can be an arbitrary time apart. Brilliant solution that, really. Thanks, tglx -- 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/