From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60235) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gRd4x-00040l-9V for qemu-devel@nongnu.org; Tue, 27 Nov 2018 08:07:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gRd4s-0007Qr-S9 for qemu-devel@nongnu.org; Tue, 27 Nov 2018 08:07:02 -0500 References: <20181127114102.4319-1-david@redhat.com> From: Thomas Huth Message-ID: <55d945eb-a9ba-9183-9c47-3a1e505d2d35@redhat.com> Date: Tue, 27 Nov 2018 14:06:46 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v1] s390x/tod: properly stop the KVM TOD while the guest is not running List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger , David Hildenbrand , qemu-devel@nongnu.org Cc: qemu-s390x@nongnu.org, Janosch Frank , Cornelia Huck , Richard Henderson On 2018-11-27 13:43, Christian Borntraeger wrote: > On 27.11.2018 12:41, David Hildenbrand wrote: >> Just like on other architectures, we should stop the clock while the guest >> is not running. This is already properly done for TCG. Right now, doing an >> offline migration (stop, migrate, cont) can easily trigger stalls in the >> guest. >> >> Even doing a >> (hmp) stop >> ... wait 2 minutes ... >> (hmp) cont >> will already trigger stalls. >> >> So whenever the guest stops, backup the KVM TOD. When continuning to run >> the guest, restore the KVM TOD. > > We do a similar thing for managedsave so it probably makes sense to solve > the stall warnings. Now: At the same time, we actually want to have the guest > see the real time and maybe even share the TOD clock with the host in some > way, while at the same time avoid the stall warnings. Hmm, by the way, do we also have to consider the "-rtc clock=host|rt|vm" option from the commandl line, or is this an orthogonal concept? Thomas