From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.91] helo=mail.sourceforge.net) by sc8-sf-list1-new.sourceforge.net with esmtp (Exim 4.43) id 1K3cnd-0004YV-Ow for user-mode-linux-devel@lists.sourceforge.net; Tue, 03 Jun 2008 13:08:06 -0700 Received: from smtp1.linux-foundation.org ([140.211.169.13]) by mail.sourceforge.net with esmtps (TLSv1:AES256-SHA:256) (Exim 4.44) id 1K3cnc-00054R-DO for user-mode-linux-devel@lists.sourceforge.net; Tue, 03 Jun 2008 13:08:05 -0700 Date: Tue, 3 Jun 2008 13:07:09 -0700 From: Andrew Morton Message-Id: <20080603130709.fcf6a751.akpm@linux-foundation.org> In-Reply-To: <878wxmfg99.fsf@hades.wkstn.nix> References: <20080603190235.GA9511@c2.user-mode-linux.org> <20080603123211.e129c222.akpm@linux-foundation.org> <200806031543.56864.dhazelton@enter.net> <878wxmfg99.fsf@hades.wkstn.nix> Mime-Version: 1.0 Subject: Re: [uml-devel] [PATCH 1/6] UML - Deal with host time going backwards List-Id: The user-mode Linux development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: user-mode-linux-devel-bounces@lists.sourceforge.net Errors-To: user-mode-linux-devel-bounces@lists.sourceforge.net To: Nix Cc: jdike@addtoit.com, linux-kernel@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, dhazelton@enter.net On Tue, 03 Jun 2008 20:52:18 +0100 Nix wrote: > On 3 Jun 2008, Daniel Hazelton said: > > > On Tuesday 03 June 2008 03:32:11 pm Andrew Morton wrote: > >> On Tue, 3 Jun 2008 15:02:35 -0400 > >> > >> Jeff Dike wrote: > >> > Protection against the host's time going backwards - keep track of the > >> > time at the last tick and if it's greater than the current time, keep > >> > time stopped until the host catches up. > >> > >> Strange. What would cause the host's time (or at least UML's perception > >> of it) to go backwards? > > > > A wild guess would be that the UML process is running "fast" at some point and > > its expectation of the host's time is skewed forward because of that. > > Quite so. Simply running ntp on the host (in slew-only mode, no less!) > can cause this. > > > Another possibility is that the hosts clock got reset between the times UML > > has checked it and the correction was a negative one. > > That too. > So if I change the host's time by an hour, the time will not advance at all on the guest for the next hour? Sounds suboptimal :) I suppose the guest should be running an ntp client synced to something sane anyway? ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758430AbYFCUIS (ORCPT ); Tue, 3 Jun 2008 16:08:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754896AbYFCUIH (ORCPT ); Tue, 3 Jun 2008 16:08:07 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57157 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754819AbYFCUIG (ORCPT ); Tue, 3 Jun 2008 16:08:06 -0400 Date: Tue, 3 Jun 2008 13:07:09 -0700 From: Andrew Morton To: Nix Cc: dhazelton@enter.net, jdike@addtoit.com, linux-kernel@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net Subject: Re: [PATCH 1/6] UML - Deal with host time going backwards Message-Id: <20080603130709.fcf6a751.akpm@linux-foundation.org> In-Reply-To: <878wxmfg99.fsf@hades.wkstn.nix> References: <20080603190235.GA9511@c2.user-mode-linux.org> <20080603123211.e129c222.akpm@linux-foundation.org> <200806031543.56864.dhazelton@enter.net> <878wxmfg99.fsf@hades.wkstn.nix> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 03 Jun 2008 20:52:18 +0100 Nix wrote: > On 3 Jun 2008, Daniel Hazelton said: > > > On Tuesday 03 June 2008 03:32:11 pm Andrew Morton wrote: > >> On Tue, 3 Jun 2008 15:02:35 -0400 > >> > >> Jeff Dike wrote: > >> > Protection against the host's time going backwards - keep track of the > >> > time at the last tick and if it's greater than the current time, keep > >> > time stopped until the host catches up. > >> > >> Strange. What would cause the host's time (or at least UML's perception > >> of it) to go backwards? > > > > A wild guess would be that the UML process is running "fast" at some point and > > its expectation of the host's time is skewed forward because of that. > > Quite so. Simply running ntp on the host (in slew-only mode, no less!) > can cause this. > > > Another possibility is that the hosts clock got reset between the times UML > > has checked it and the correction was a negative one. > > That too. > So if I change the host's time by an hour, the time will not advance at all on the guest for the next hour? Sounds suboptimal :) I suppose the guest should be running an ntp client synced to something sane anyway?