From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40819) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fPsmn-0006Rs-El for qemu-devel@nongnu.org; Mon, 04 Jun 2018 12:56:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fPsmj-0000i6-6i for qemu-devel@nongnu.org; Mon, 04 Jun 2018 12:56:49 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39162 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fPsmi-0000gN-Tx for qemu-devel@nongnu.org; Mon, 04 Jun 2018 12:56:45 -0400 Date: Mon, 4 Jun 2018 17:56:37 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180604165637.GP19749@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20180603092749.107476-1-marcel.apfelbaum@gmail.com> <20180604042928-mutt-send-email-mst@kernel.org> <20180604125415.GN7451@localhost.localdomain> <20180604130129.GG19749@redhat.com> <20180604194500-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180604194500-mutt-send-email-mst@kernel.org> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH RFC] hw/pc: set q35 as the default x86 machine List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Eduardo Habkost , pbonzini@redhat.com, qemu-devel@nongnu.org, rth@twiddle.net On Mon, Jun 04, 2018 at 07:48:51PM +0300, Michael S. Tsirkin wrote: > On Mon, Jun 04, 2018 at 02:01:29PM +0100, Daniel P. Berrang=C3=A9 wrote= : > > On Mon, Jun 04, 2018 at 09:54:15AM -0300, Eduardo Habkost wrote: > > > On Mon, Jun 04, 2018 at 04:38:22AM +0300, Michael S. Tsirkin wrote: > > > > On Sun, Jun 03, 2018 at 12:27:49PM +0300, Marcel Apfelbaum wrote: > > > > > Moving to QEMU 3.0 seems like a good opportunity for such a cha= nge. > > > > >=20 > > > > > I440FX is really old and does not support modern features like = IOMMU. > > > > > Q35's SATA emulation is faster than pc's IDE, native PCI expres= s hotplug > > > > > is cleaner than ACPI based one and so on... > > > > >=20 > > > > > Also the libvirt guys added very good support for the Q35 machi= ne (thanks!). > > > > >=20 > > > > > Management software should always specify the machine type and = for the > > > > > current setups, adding '-machine pc' to the command line is not= such a > > > > > big deal. > > > > >=20 > > > > > In time the pc machine will fade out and we will probably stop = adding > > > > > new versions at some point. > > > > >=20 > > > > > Signed-off-by: Marcel Apfelbaum > > > >=20 > > > > For command line users, I think changing the default isn't nice. > > > >=20 > > > > Yes it's easy to add -machine pc but there's no documentation > > > > that tells you to do so. Add to that shortcuts like -cdrom > > > > stop working, hotplug needs extra bridges to work, and one > > > > can see that while management tool users benefit from q35, > > > > command line users will suffer. > > > >=20 > > > > Can't we add a tag for management without changing the command li= ne > > > > default? How about "management-default"? "recommended"? "latest"? > > >=20 > > > We could add new aliases if they are useful for management > > > software, but we would need a well-defined use case and set of > > > requirements+expectations for the new alias. > >=20 > > I'm not convinced by the idea of adding a distinct default "for mgmt"= . All > > the problems described wrt 'q35' vs 'pc' apply equally to management = apps > > as they do to humans. It just happens that one common mgmt layer (lib= virt) > > knows how to handle some of the complexity of q35. Other mgmt apps th= ough > > are just as likely to be hurt by the change as humans are. So effecti= vely > > the proposed "for mgmt" is actually "for libvirt >=3D some version",= which > > feels like a layering violation to me. >=20 > Is libvirt happy to just hard-code q35 for now then? I'm pretty wary of doing that, as I feel 'pc' has broader OS compatibilit= y than 'q35', so we'd be likely to cause breakage for users. IMHO, defaults are something better expressed in libosinfo, so if there's guests where we think q35 is a better choice, we can record it there and leave everything else on pc to avoid risk of breakage. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|