From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57778) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bUUpK-0006g4-Ow for qemu-devel@nongnu.org; Tue, 02 Aug 2016 04:13:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bUUpH-0007LP-C7 for qemu-devel@nongnu.org; Tue, 02 Aug 2016 04:13:26 -0400 Date: Tue, 2 Aug 2016 10:13:19 +0200 From: Igor Mammedov Message-ID: <20160802101319.3eaf6a79@nial.brq.redhat.com> In-Reply-To: <20160802062050.GZ2588@voom.fritz.box> References: <1470111908-8456-1-git-send-email-david@gibson.dropbear.id.au> <20160802050434.GC16350@in.ibm.com> <20160802062050.GZ2588@voom.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] spapr: Don't support query-hotpluggable-cpus on earlier pseries machine types List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: Bharata B Rao , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, agraf@suse.de, pkrempa@redhat.com On Tue, 2 Aug 2016 16:20:50 +1000 David Gibson wrote: > On Tue, Aug 02, 2016 at 10:34:34AM +0530, Bharata B Rao wrote: > > On Tue, Aug 02, 2016 at 02:25:08PM +1000, David Gibson wrote: > > > On Power, support for vCPU hotplug is new in qemu 2.7. However, we > > > currently implement the query_hotpluggable_cpus hook the same for all > > > pseries machine type versions. > > > > > > However, the old-style CPU initialization doesn't work with the new query > > > code, meaning that attempting to use query-hotpluggable-cpus on a > > > pseries-2.6 or earlier VM will cause qemu to SEGV. > > > > > > This fixes the problem by simply disabling the hook for earlier machine > > > types. > > > > I had sent a patch to fix this and a couple of other related issues > > some time back and it indeed was accepted into your ppc-for-2.7 branch. > > > > https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg01539.html > > > > Only now I am realizing that somehow that patch didn't make it to mainline. > > Oh.. good point. Sorry, that one somehow slipped through the cracks. > > So, the remaining question is, what's the preferred behaviour for > older machine types: > > 1) should query-hotpluggable-cpus give an error, the same as it does > on machine types which have never supported it (this is what my > patch does) > > or > > 2) Should query-hotpluggable-cpus succeed, but return an empty list? > (this is what Bharata's patch does) > > Igor and / or Peter, do you have an opinion on which behaviour is preferable? > If it doesn't have any output then it makes sense to set handler to NULL so it would return error.