From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:48224) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UQHuU-0003eB-2P for qemu-devel@nongnu.org; Thu, 11 Apr 2013 09:51:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UQHuR-0002s7-Hf for qemu-devel@nongnu.org; Thu, 11 Apr 2013 09:51:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1986) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UQHuR-0002s0-8m for qemu-devel@nongnu.org; Thu, 11 Apr 2013 09:51:27 -0400 Date: Thu, 11 Apr 2013 16:51:21 +0300 From: "Michael S. Tsirkin" Message-ID: <20130411135121.GB24942@redhat.com> References: <1365632901-15470-1-git-send-email-mrhines@linux.vnet.ibm.com> <1365632901-15470-11-git-send-email-mrhines@linux.vnet.ibm.com> <20130411073843.GB19601@redhat.com> <51667FEE.903@redhat.com> <20130411111329.GA21714@redhat.com> <5166B86F.1050504@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5166B86F.1050504@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael R. Hines" Cc: aliguori@us.ibm.com, qemu-devel@nongnu.org, owasserm@redhat.com, abali@us.ibm.com, mrhines@us.ibm.com, gokul@us.ibm.com, Paolo Bonzini On Thu, Apr 11, 2013 at 09:19:43AM -0400, Michael R. Hines wrote: > On 04/11/2013 07:13 AM, Michael S. Tsirkin wrote: > >On Thu, Apr 11, 2013 at 11:18:38AM +0200, Paolo Bonzini wrote: > >>Il 11/04/2013 09:38, Michael S. Tsirkin ha scritto: > >>>On Wed, Apr 10, 2013 at 06:28:18PM -0400, mrhines@linux.vnet.ibm.com wrote: > >>>>From: "Michael R. Hines" > >>>> > >>>>This allows the user to disable zero page checking during migration > >>>> > >>>>Signed-off-by: Michael R. Hines > >>>IMO this knob is too low level to expose to management. > >>>Why not disable this automatically when migrating with rdma? > >>Thinking more about it, I'm not sure why it is important to disable it. > >This just illustrates the point. There's no place for such low level > >knobs in the management interface. > > > > I disagree with that: We already have precedent for this in the > XBZRLE capability. My understanding is the issue is protocol compatibility, not optimization. E.g. you can migrate to file, for each new feature you need a way to disable it to stay compatible. > Zero page checking is no "more" low-level than this > capability already is and the community has already agreed to expose > this capability to management. > > Since zero page scanning does in fact affect performance, we not give > the user the option? > > Why would the community agree to expose one low-level feature and > not expose another? > > - Michael