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Thu, 14 May 2020 15:55:43 +0000 (UTC) Date: Thu, 14 May 2020 16:55:40 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Paolo Bonzini Subject: Re: proposal: deprecate -readconfig/-writeconfig Message-ID: <20200514155540.GN1280939@redhat.com> References: <7599153e-89a2-9a86-16ad-4a3c6a107b18@redhat.com> <20200514085622.GB1280939@redhat.com> <56379563-c1f3-3270-f9ac-5bdd49b324aa@redhat.com> <20200514153456.GL1280939@redhat.com> <93bda646-6f5f-69b6-57ec-36ec9485e84c@redhat.com> MIME-Version: 1.0 In-Reply-To: <93bda646-6f5f-69b6-57ec-36ec9485e84c@redhat.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/14 11:31:36 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FROM_EXCESS_BASE64=0.979, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , John Snow , qemu-devel , Markus Armbruster Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, May 14, 2020 at 05:51:02PM +0200, Paolo Bonzini wrote: > On 14/05/20 17:34, Daniel P. Berrangé wrote: > > Yeah, the key thing is that you really want to be able to provide the > > whole initial config in one go as an atomic action. I don't want to > > issue 100 individual QMP commands to load each initial device. > > Why? I think if we do something like the qemu-vm-$TARGET that you > propose below, there's absolutely no difference between the two. Ok, I should clarify. I don't want to do 100 individual serialized round-trip request+reply, as that'd create latency on startup. 100 pipelined/parallelized request+reply would be ok, as you'll not have the synchronization delay for each command. Today the biggest cause of slow startup in libvirt, is issuing something like 100+ serialized QMP calls to check status of individual CPUID features. Possibly this is already just a libvirt bug we can could just stuff all 100 qom-get queries down the pipe in one go and have 1 wait for replies to arrive. > Then you'd have a > > qemu-run /some/file.yaml > > (notice the lack of $TARGET) that takes care of starting the VM. > > > I tend to think we'd be better served by focusing on introducing a new set > > of binaries, qemu-vm-$TARGET, which exclusively use a new config syntax, > > free of any legacy baggage present in qemu-system-$TARGET. > > > > Work on qemu-vm-$TARGET will involve refactoring, and that will certainly > > risk causing bugs in qemu-system-$TARGET. The premise though is that this > > risk is lower, than if we tried to retrofit a new config syuntax directly > > into qemu-system-$TARGET. > > > > In particular I think it is basically impossible to do any meaningful > > changes in the main() method of softmmu/vl.c, due to the fragile ordering > > for creation of various different devices/backends, and its interaction > > with the argv parsing. By using a new qemu-vm-$TARGET we can have a new > > softmmu/vm.c, instead of vl.c. We'll still likely need to modify parts of > > vl.c to use new/changed API calls, but that's less distruptive, as we > > can leave the crazy logic for ordering of device creation untouched. > > Agreed. > > Paolo > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|