From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35333) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f8ZUD-00069R-3M for qemu-devel@nongnu.org; Tue, 17 Apr 2018 18:54:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f8ZU9-0006SX-64 for qemu-devel@nongnu.org; Tue, 17 Apr 2018 18:54:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50744) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f8ZU8-0006Qh-SU for qemu-devel@nongnu.org; Tue, 17 Apr 2018 18:54:01 -0400 Date: Tue, 17 Apr 2018 19:53:54 -0300 From: Eduardo Habkost Message-ID: <20180417225354.GI29865@localhost.localdomain> References: <20171010003951-mutt-send-email-mst@kernel.org> <20171010083143.GA30015@redhat.com> <20171010150628.GI30015@redhat.com> <20171010180110.GI3246@localhost.localdomain> <20171015044800-mutt-send-email-mst@kernel.org> <20171020184820.GP2942@localhost.localdomain> <20180417211126.GD29865@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v6 2/7] hw/misc: add vmcoreinfo device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cole Robinson Cc: "Michael S. Tsirkin" , QEMU , Dave Anderson , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Martin Kletzander , Igor Mammedov , Laszlo Ersek On Tue, Apr 17, 2018 at 06:31:57PM -0400, Cole Robinson wrote: > On 04/17/2018 05:11 PM, Eduardo Habkost wrote: > > On Tue, Apr 17, 2018 at 03:12:03PM -0400, Cole Robinson wrote: > > [...] > >> Reviving this... did any follow up changes happen? > >> > >> Marc-Andr=E9 patched virt-manager a few months back to enable -devic= e > >> vmcoreinfo for new VMs: > >> > >> https://www.redhat.com/archives/virt-tools-list/2018-February/msg000= 20.html > >> > >> And I see there's at least a bug tracking adding this to openstack f= or > >> new VMs: > >> > >> https://bugzilla.redhat.com/show_bug.cgi?id=3D1555276 > >> > >> If this feature doesn't really have any downsides, it would be nice = to > >> get this tied to new machine types. Saves a lot of churn for higher > >> levels of the stack > >=20 > > I understand this would be nice to have considering the existing > > stacks, but at the same time I would like the rest of the > > stack(s) to really try to not depend on QEMU machine-types to > > define policy/defaults. > >=20 > > Every feature that is hidden behind an opaque machine-type name > > and not visible in the domain XML and QEMU command-line increases > > the risk of migration and compatibility bugs. > >=20 >=20 > What exactly is the migration compatibility issue with turning on the > equivalent of -device vmcoreinfo for -M *-2.13+ ? Possibly prevents > backwards migration to older qemu but is that even a goal? I mean the extra migration compatibility code that needs to be maintained on older machine-types. It's extra maintenance burden on both upstream and downstream QEMU trees. >=20 > > This was being discussed in a mail thread at: > > https://www.mail-archive.com/ovirt-devel@redhat.com/msg01196.html > >=20 > > Quoting Daniel, on that thread: > >=20 > > ] Another case is the pvpanic device - while in theory that could > > ] have been enabled by default for all guests, by QEMU or a config > > ] generator library, doing so is not useful on its own. The hard > > ] bit of the work is adding code to the mgmt app to choose the > > ] action for when pvpanic triggers, and code to handle the results > > ] of that action. > >=20 > > From that comment, I understand that simply making QEMU create a > > pvpanic device by default on pc-2.13+ won't be useful at all? > >=20 >=20 > This qemu-devel thread was about -device vmcoreinfo though, not pvpanic= . > vmcoreinfo doesn't need anything else to work AFAICT and shouldn't need > any explicit config, heck it doesn't even have any -device properties. >=20 > Like Dan says pvpanic isn't a 'just works' thing, and I know for window= s > VMs it shows up in device manager which has considerations for things > like SVVP. I think vmcoreinfo doesn't have the same impact >=20 Oops, nevermind. I confused both. > There are some guest visible things that we have turned on for new > machine types in the past, pveoi and x2apic comes to mind. Yes, we have tons of guest-visible things that we tie to the machine-type. What I'm looking for is a solution to make this less frequent in the future. --=20 Eduardo