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[83.35.20.18]) by smtp.gmail.com with ESMTPSA id y3sm132210wrq.30.2019.07.02.15.04.03 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 02 Jul 2019 15:04:03 -0700 (PDT) Date: Wed, 3 Jul 2019 00:04:00 +0200 From: Sergio Lopez To: Peter Maydell Message-ID: <20190702220400.GA13923@localhost> References: <20190702121106.28374-1-slp@redhat.com> <87a7dwnxwj.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.128.67 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: Eduardo Habkost , maran.wilson@oracle.com, "Michael S. Tsirkin" , 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 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.