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Tsirkin" To: Thomas Huth Subject: Re: [PATCH 3/3] x86: Switch to q35 as the default machine type Message-ID: <20220217025108-mutt-send-email-mst@kernel.org> References: <20220215162537.605030-1-dgilbert@redhat.com> <20220215162537.605030-4-dgilbert@redhat.com> <20220216105808.77kqhmsagz3ej74h@sirius.home.kraxel.org> <45e4f959-8f04-3baf-5e95-d23ed62e4b27@redhat.com> MIME-Version: 1.0 In-Reply-To: <45e4f959-8f04-3baf-5e95-d23ed62e4b27@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.083, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: eduardo@habkost.net, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , quintela@redhat.com, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Gerd Hoffmann , pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Feb 17, 2022 at 08:46:55AM +0100, Thomas Huth wrote: > On 16/02/2022 18.57, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > > On Wed, Feb 16, 2022 at 05:40:44PM +0000, Dr. David Alan Gilbert wrote: > > > > * Thomas Huth (thuth@redhat.com) wrote: > > > > > On 16/02/2022 12.01, Dr. David Alan Gilbert wrote: > > > > > > * Gerd Hoffmann (kraxel@redhat.com) wrote: > > > > > > > Hi, > > > > > > > > Given the semantic differences from 'i440fx', changing the default > > > > > > > > machine type has effects that are equivalent to breaking command > > > > > > > > line syntax compatibility, which is something we've always tried > > > > > > > > to avoid. > > > > > > > > > > > > > > And if we are fine breaking backward compatibility I'd rather *not* pick > > > > > > > a default, effectively making -M $something mandatory, similar to arm. > > > > > > > > > > > > Oh, that's probably easy to do; what are other peoples thoughts on > > > > > > that? > > > > > > > > > > I agree with Gerd. Getting rid of a default machine on x86 is likely better > > > > > than silently changing it to q35. But I'd maybe say that this should go > > > > > through the deprecation process first? > > > > > > > > So just adding something like the following under 'System emulator > > > > machines': > > > > > > > > x86 default machine type > > > > ------------------------ > > > > > > > > x86 currently defaults to the very old ```pc``` machine type > > > > which is based on the very old ```i440f``` chipset. This default > > > > will be removed and the user will be required to specify a machine > > > > type explicitly using -M; users are encouraged to switch to the > > > > not quite as old ```q35``` machine types. > > > > > > > > > > > > (This option is going to take a lot more work switching all the > > > > test cases over; in my world here I'd only changed the tests that broke > > > > on q35, now everything is going to need to specify a type). > > > > > > ....which is still nothing compared to how many users will be impacted > > > and the docs all over the internet we'll never be able to change, which > > > give illustrations using qemu command lines without '-M pc' > > > > What's your prreference - it sounds like you'd prefer to leave the > > default as 'pc' ? > > > > aarch's message is: > > qemu-system-aarch64: No machine specified, and there is no default > > Use -machine help to list supported machines > > > > We could add a: > > 'Use -machine pc for the old default behaviour' > > Sounds like a good idea, but then I'd also do: > > 'Use -M pc for the old default behaviour, or -M q35 for a more modern > machine' or so. > > Thomas > How about we start by going through a deprecation period then? Make attempts to create a machine without -machine produce a warning for a couple of cycles. -- MST