From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34032) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ftA0Z-0005Ma-Fn for qemu-devel@nongnu.org; Fri, 24 Aug 2018 07:12:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ftA0N-00084t-Uy for qemu-devel@nongnu.org; Fri, 24 Aug 2018 07:12:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39630) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ftA0N-00084I-Mm for qemu-devel@nongnu.org; Fri, 24 Aug 2018 07:11:51 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D5F593091742 for ; Fri, 24 Aug 2018 11:11:50 +0000 (UTC) Date: Fri, 24 Aug 2018 08:11:48 -0300 From: Eduardo Habkost Message-ID: <20180824111148.GX3778@localhost.localdomain> References: <1535035877-219196-1-git-send-email-imammedo@redhat.com> <20180824111350.04d10250@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180824111350.04d10250@redhat.com> Subject: Re: [Qemu-devel] [PATCH] vl.c: make sure maxcpus matches topology to prevent migration failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Paolo Bonzini , qemu-devel@nongnu.org, dgilbert@redhat.com On Fri, Aug 24, 2018 at 11:13:50AM +0200, Igor Mammedov wrote: > On Thu, 23 Aug 2018 18:32:41 +0200 > Paolo Bonzini wrote: > > > On 23/08/2018 16:51, Igor Mammedov wrote: > > > Topology (threads*cores*sockets) must match maxcpus to be valid, > > > otherwise we could start QEMU with invalid topology that throws > > > a error on migration destination side, that should not be reachable: > > > Source: > > > -smp 8,maxcpus=64,cores=1,threads=8,sockets=1 > > > // hotplug cpus upto maxcpus > > > Destination: > > > -smp 64,maxcpus=64,cores=1,threads=8,sockets=1 > > > qemu: cpu topology: sockets (1) * cores (1) * threads (8) < smp_cpus (64) > This destination CLI aren't exactly correct as well since > it should've been exactly the same -smp as on source + a bunch of -device cpufoo... > so we can always say go fix your CLI so it won't trigger error. > > > The destination should have sockets=8, shouldn't it? > either that or cores=8 or cores=4,sockets=2 ... > > > It seems to me that, at startup, you should have cpus = s*t*c and cpus > > <= maxcpus. Currently we check cpus <= s*t*c <= maxcpus, which doesn't > > make much sense. > I think that s*t*c should describe topology of whole machine > including not yet plugged vcpus. "cpus = s*t*c" probably won't work > for partially filled package case: > -smp 1,cores=1,threads=8,sockets=1 > cores/threads should reflect full package configuration > for guest to see an expected topology. Oh, now I remember: that's the reason we don't enforce s*t*c == smp_cpus nor s*t*c == max_cpus. Both "-smp 4,maxcpus=8,cores=2,threads=2,sockets=1" and "-smp 4,maxcpus=8,cores=2,threads=2,sockets=2" worked since maxcpus was introduced, making the semantics of "sockets" unclear and hard to change without breaking existing configs. -- Eduardo