On Tue, 2 Jul 2019 at 18:34, Sergio Lopez <s...@redhat.com> wrote: > Peter Maydell <peter.mayd...@linaro.org> 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 thanks -- PMM
