From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward Date: Tue, 06 May 2014 09:11:57 +0200 Message-ID: <53688B3D.7030905@suse.de> References: <1399297882-3444-1-git-send-email-agraf@suse.de> <5367CE81.6030506@beyond.pl> <5367D7BC.2040705@beyond.pl> <20140505232710.GB20638@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" To: Marcelo Tosatti , =?UTF-8?B?TWFyY2luIEdpYnXFgmE=?= Return-path: Received: from cantor2.suse.de ([195.135.220.15]:57251 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933838AbaEFHL7 (ORCPT ); Tue, 6 May 2014 03:11:59 -0400 In-Reply-To: <20140505232710.GB20638@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: 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,= VM freezes for couple of hours and then resumes with date few hundreds= years ahead. Happens only with kvmclock. >>>> >>>> And this patch seems to fix very similar issue so maybe it's all t= he same bug. >>> I'm fairly sure it is the exact same bug. Jumping backward is like = jumping 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. =46or the 3.0 case the host clock source is TSC. Alex