Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932246AbaJNNTm (ORCPT ); Tue, 14 Oct 2014 09:19:42 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:59908 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755229AbaJNNTl (ORCPT ); Tue, 14 Oct 2014 09:19:41 -0400 Date: Tue, 14 Oct 2014 15:19:35 +0200 From: Richard Cochran To: Thomas Shao Cc: "tglx@linutronix.de" , "gregkh@linuxfoundation.org" , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "jasowang@redhat.com" , KY Srinivasan Subject: Re: [PATCH 2/2] hyperv: Implement Time Synchronization using host time sample Message-ID: <20141014131935.GA5994@localhost.localdomain> References: <1413285078-7027-1-git-send-email-huishao@microsoft.com> <20141014115412.GC4019@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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, Oct 14, 2014 at 01:04:35PM +0000, Thomas Shao wrote: > > > + /* > > > + * Use the Hyper-V time sample to adjust the guest time. The > > > + * algorithm is: If the sample offsets exceeds 1 second, we > > > + * directly set the clock to the server time. If the offset is > > > > So the guests will experience random time jumps in the kernel, without any > > rhyme or reason? > > This behavior is designed for some extreme cases. Like manually setting guest time > to some value. Or the host resumes from a hibernate state. Normally, we should not > run into this. But when it *does* happen, the guest software will have no way of knowing what happened. That stinks. Taking your example, when the guest sets its time, the time will suddenly jump somewhere else, and for no apparent reason. >From the guest's point of view, this is really not acceptable. Thanks, Richard -- 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/