From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49980) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNvmW-0002cn-Fj for qemu-devel@nongnu.org; Fri, 15 Jul 2016 01:35:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bNvmS-0000J2-Bn for qemu-devel@nongnu.org; Fri, 15 Jul 2016 01:35:23 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:58983 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNvmS-0000Ii-74 for qemu-devel@nongnu.org; Fri, 15 Jul 2016 01:35:20 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u6F5XTMx121817 for ; Fri, 15 Jul 2016 01:35:18 -0400 Received: from e28smtp07.in.ibm.com (e28smtp07.in.ibm.com [125.16.236.7]) by mx0b-001b2d01.pphosted.com with ESMTP id 246hekvt6d-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 15 Jul 2016 01:35:18 -0400 Received: from localhost by e28smtp07.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 15 Jul 2016 11:05:13 +0530 Date: Fri, 15 Jul 2016 11:05:05 +0530 From: Bharata B Rao Reply-To: bharata@linux.vnet.ibm.com References: <1468392620-25599-1-git-send-email-bharata@linux.vnet.ibm.com> <20160714005127.GH14615@voom.fritz.box> <20160714102715.303950e4@nial.brq.redhat.com> <20160715052901.GW14615@voom.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160715052901.GW14615@voom.fritz.box> Message-Id: <20160715053505.GA7036@in.ibm.com> Subject: Re: [Qemu-devel] [PATCH 1/1] spapr: Ensure CPU cores are added contiguously and removed in LIFO order List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: Igor Mammedov , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, groug@kaod.org On Fri, Jul 15, 2016 at 03:29:01PM +1000, David Gibson wrote: > On Thu, Jul 14, 2016 at 10:27:15AM +0200, Igor Mammedov wrote: > > On Thu, 14 Jul 2016 10:51:27 +1000 > > David Gibson wrote: > > > > > On Wed, Jul 13, 2016 at 12:20:20PM +0530, Bharata B Rao wrote: > > > > If CPU core addition or removal is allowed in random order leading to > > > > holes in the core id range (and hence in the cpu_index range), migration > > > > can fail as migration with holes in cpu_index range isn't yet handled > > > > correctly. > > > > > > > > Prevent this situation by enforcing the addition in contiguous order > > > > and removal in LIFO order so that we never end up with holes in > > > > cpu_index range. > > > > > > > > Signed-off-by: Bharata B Rao > > > > --- > > > > While there is work in progress to support migration when there are holes > > > > in cpu_index range resulting from out-of-order plug or unplug, this patch > > > > is intended as a last resort if no easy, risk-free and elegant solution > > > > emerges before 2.7 dev cycle ends. > > > > > > Applied to ppc-for-2.7. We can revert it once the problems with > > > cpu_index are sorted out. > > You'd need to add machine type specific compat option here, > > so that new-qemu -M 2.7 wouldn't allow out of order too and > > could be migrated to old-qemu -M 2.7 > > Hmm, do we care about migration from newer back to older versions of > qemu upstream? If so, then I guess we do need this option. Though > strictly we don't need it until we actually do allow any-order > hotplug. Right. I too thought that when we relax this restriction say in 2.8, we could have a sPAPRMachineClass option to allow out-of-order hotplug for 2.8 upwards and disable it for 2.7 downwards. With this, 2.7 guest started with new-qemu can be migrated to old-qemu. Regards, Bharata.