From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45292) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WhZXq-0008An-R5 for qemu-devel@nongnu.org; Tue, 06 May 2014 03:12:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WhZXj-00080O-6O for qemu-devel@nongnu.org; Tue, 06 May 2014 03:12:06 -0400 Received: from cantor2.suse.de ([195.135.220.15]:53523 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WhZXi-00080C-Vd for qemu-devel@nongnu.org; Tue, 06 May 2014 03:11:59 -0400 Message-ID: <53688B3D.7030905@suse.de> Date: Tue, 06 May 2014 09:11:57 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1399297882-3444-1-git-send-email-agraf@suse.de> <5367CE81.6030506@beyond.pl> <5367D7BC.2040705@beyond.pl> <20140505232710.GB20638@amt.cnet> In-Reply-To: <20140505232710.GB20638@amt.cnet> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcelo Tosatti , =?UTF-8?B?TWFyY2luIEdpYnXFgmE=?= Cc: "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" On 06.05.14 01:27, Marcelo Tosatti wrote: > On Mon, May 05, 2014 at 08:26:04PM +0200, Marcin Gibu=C5=82a wrote: >>>> is it possible to have kvmclock jumping forward? >>>> >>>> Because I've reproducible case when at about 1 per 20 vm restores, V= M freezes for couple of hours and then resumes with date few hundreds yea= rs ahead. Happens only with kvmclock. >>>> >>>> And this patch seems to fix very similar issue so maybe it's all the= same bug. >>> I'm fairly sure it is the exact same bug. Jumping backward is like ju= mping forward by a biiiiig amount :) >> Hi, >> >> I've tested your path on my test VM... don't know if it's pure luck >> or not, but it didn't hang with over 70 restores. >> >> The message "KVM Clock migrated backwards, using later time" fires >> every time, but VM is healthy after resume. > What is the host clocksource? (cat > /sys/devices/system/clocksource/clocksource0/current_clocksource). > > And kernel version? I've seen 3 different reports of this bug by now. One is Marcin where I=20 don't have any details. One is running 3.0 plus patches and another one=20 is running 3.14. For the 3.0 case the host clock source is TSC. Alex