From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36509) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fPuP4-0005la-Cw for qemu-devel@nongnu.org; Mon, 04 Jun 2018 14:40:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fPuOz-0000UN-GJ for qemu-devel@nongnu.org; Mon, 04 Jun 2018 14:40:26 -0400 Received: from mail-wr0-x241.google.com ([2a00:1450:400c:c0c::241]:40793) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1fPuOz-0000Si-8A for qemu-devel@nongnu.org; Mon, 04 Jun 2018 14:40:21 -0400 Received: by mail-wr0-x241.google.com with SMTP id l41-v6so45246655wre.7 for ; Mon, 04 Jun 2018 11:40:21 -0700 (PDT) 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> <20180604165637.GP19749@redhat.com> From: Marcel Apfelbaum Message-ID: Date: Mon, 4 Jun 2018 21:40:15 +0300 MIME-Version: 1.0 In-Reply-To: <20180604165637.GP19749@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US 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: "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , "Michael S. Tsirkin" Cc: pbonzini@redhat.com, rth@twiddle.net, Eduardo Habkost , qemu-devel@nongnu.org On 06/04/2018 07:56 PM, Daniel P. Berrangé wrote: > 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. Berrangé 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 change. >>>>>> >>>>>> I440FX is really old and does not support modern features like IOMMU. >>>>>> Q35's SATA emulation is faster than pc's IDE, native PCI express hotplug >>>>>> is cleaner than ACPI based one and so on... >>>>>> >>>>>> Also the libvirt guys added very good support for the Q35 machine (thanks!). >>>>>> >>>>>> 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. >>>>>> >>>>>> In time the pc machine will fade out and we will probably stop adding >>>>>> new versions at some point. >>>>>> >>>>>> Signed-off-by: Marcel Apfelbaum >>>>> For command line users, I think changing the default isn't nice. >>>>> >>>>> 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. >>>>> >>>>> Can't we add a tag for management without changing the command line >>>>> default? How about "management-default"? "recommended"? "latest"? >>>> 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. >>> 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 (libvirt) >>> knows how to handle some of the complexity of q35. Other mgmt apps though >>> are just as likely to be hurt by the change as humans are. So effectively >>> the proposed "for mgmt" is actually "for libvirt >= some version", which >>> feels like a layering violation to me. >> 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 compatibility > 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. The only info we need to pass properly to management systems is: "Use q35 unless your guests are really old". I agree the exiting systems should not be touched. Thanks, Marcel > Regards, > Daniel