From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45240) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X4ANP-0003ne-Va for qemu-devel@nongnu.org; Mon, 07 Jul 2014 10:58:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1X4ANI-0002CT-Fa for qemu-devel@nongnu.org; Mon, 07 Jul 2014 10:58:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58263) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X4ANI-0002CP-2l for qemu-devel@nongnu.org; Mon, 07 Jul 2014 10:58:36 -0400 Date: Mon, 7 Jul 2014 16:58:26 +0200 From: "Dr. David Alan Gilbert" Message-ID: <20140707145825.GC3443@work-vm> References: <1404495717-4239-1-git-send-email-dgilbert@redhat.com> <53B7D36B.4050800@redhat.com> <20140707140229.GA3443@work-vm> <53BAB03B.5000308@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53BAB03B.5000308@redhat.com> Subject: Re: [Qemu-devel] [PATCH 00/46] Postcopy implementation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: aarcange@redhat.com, yamahata@private.email.ne.jp, quintela@redhat.com, qemu-devel@nongnu.org, lilei@linux.vnet.ibm.com * Paolo Bonzini (pbonzini@redhat.com) wrote: > Il 07/07/2014 16:02, Dr. David Alan Gilbert ha scritto: > >>> Could you have instead a "migrate_start_postcopy" command, and leave the > >>> policy to management instead? > >Hmm; yes that is probably possible - although with the migration_set_parameter > >configuration you get the best of both worlds: > > 1) You can set the parameter to say a few seconds and let QEMU handle it > > 2) You can set the parameter really large, but (I need to check) you could > > drop the parameter later and then cause it to kick in. > > > >I also did it this way because it was similar to the way the auto-throttling > >mechanism. > > Auto-throttling doesn't let you configure when it kicks in (it doesn't even > need support from the destination side). For postcopy you would still have > a capability, like auto-throttling, just not the argument. But auto-throttling is handled automatically by qemu rather than management; and it seems right that it should be a configurable threshold. > The reason why I prefer a manual step from management, is because postcopy > is a one-way street. Suppose a newer version of management software has > started migration with postcopy configured, and then an older version is > started. It is probably an invalid thing to do, but the confusion in the > older version could be fatal and it's nice if there's an easy way to prevent > it. Hmm, the way the setup at the moment is setup the new-version would have had to start the VMs down the one way street, I'm not sure what the old software would do bad to it. Having said that, I can see some advantages - in particular knowing when it's safe to cancel. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK