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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id o71sm20544312qke.18.2019.07.25.02.59.42 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 25 Jul 2019 02:59:45 -0700 (PDT) Date: Thu, 25 Jul 2019 05:59:40 -0400 From: "Michael S. Tsirkin" To: Sergio Lopez Message-ID: <20190725055908-mutt-send-email-mst@kernel.org> References: <20190702121106.28374-1-slp@redhat.com> <87a7dwnxwj.fsf@redhat.com> <20190702220400.GA13923@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190702220400.GA13923@localhost> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.222.193 Subject: Re: [Qemu-devel] [PATCH v3 0/4] Introduce the microvm machine type 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: , Cc: Peter Maydell , Eduardo Habkost , maran.wilson@oracle.com, QEMU Developers , Gerd Hoffmann , Paolo Bonzini , Stefano Garzarella , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 03, 2019 at 12:04:00AM +0200, Sergio Lopez wrote: > On Tue, Jul 02, 2019 at 07:04:15PM +0100, Peter Maydell wrote: > > On Tue, 2 Jul 2019 at 18:34, Sergio Lopez wrote: > > > Peter Maydell writes: > > > > Could we use virtio-pci instead of virtio-mmio? virtio-mmio is > > > > a bit deprecated and tends not to support all the features that > > > > virtio-pci does. It was introduced mostly as a stopgap while we > > > > didn't have pci support in the aarch64 virt machine, and remains > > > > for legacy "we don't like to break existing working setups" rather > > > > than as a recommended config for new systems. > > > > > > Using virtio-pci implies keeping PCI and ACPI support, defeating a > > > significant part of microvm's purpose. > > > > > > What are the issues with the current state of virtio-mmio? Is there a > > > way I can help to improve the situation? > > > > Off the top of my head: > > * limitations on numbers of devices > > * no hotplug support > > * unlike PCI, it's not probeable, so you have to tell the > > guest where all the transports are using device tree or > > some similar mechanism > > * you need one IRQ line per transport, which restricts how > > many you can have > > * it's only virtio-0.9, it doesn't support any of the new > > virtio-1.0 functionality > > * it is broadly not really maintained in QEMU (and I think > > not really in the kernel either? not sure), because we'd > > rather not have to maintain two mechanisms for doing virtio > > when virtio-pci is clearly better than virtio-mmio > > Some of these are design issues, but others can be improved with a bit > of work. > > As for the maintenance burden, I volunteer myself to help with that, so > it won't have an impact on other developers and/or projects. > > Sergio. OK so please start with adding virtio 1 support. Guest bits have been ready for years now. -- MST