On Wed, Apr 19, 2017 at 11:42 AM, Wei Wang <wei.w.w...@intel.com> wrote: > On 04/19/2017 05:57 PM, Stefan Hajnoczi wrote: >> On Wed, Apr 19, 2017 at 06:38:11AM +0000, Wang, Wei W wrote: >>> >>> We made some design changes to the original vhost-pci design, and want to >>> open >>> a discussion about the latest design (labelled 2.0) and its extension >>> (2.1). >>> 2.0 design: One VM shares the entire memory of another VM >>> 2.1 design: One VM uses an intermediate memory shared with another VM for >>> packet transmission. >> >> Hi, >> Can you talk a bit about the motivation for the 2.x design and major >> changes compared to 1.x? > > > 1.x refers to the design we presented at KVM Form before. The major > change includes: > 1) inter-VM notification support > 2) TX engine and RX engine, which is the structure built in the driver. From > the device point of view, the local rings of the engines need to be > registered.
It would be great to support any virtio device type. The use case I'm thinking of is networking and storage appliances in cloud environments (e.g. OpenStack). vhost-user doesn't fit nicely because users may not be allowed to run host userspace processes. VMs are first-class objects in compute clouds. It would be natural to deploy networking and storage appliances as VMs using vhost-pci. In order to achieve this vhost-pci needs to be a virtio transport and not a virtio-net-specific PCI device. It would extend the VIRTIO 1.x spec alongside virtio-pci, virtio-mmio, and virtio-ccw. When you say TX and RX I'm not sure if the design only supports virtio-net devices? > The motivation is to build a common design for 2.0 and 2.1. > >> >> What is the relationship between 2.0 and 2.1? Do you plan to upstream >> both? > > 2.0 and 2.1 use different ways to share memory. > > 2.0: VM1 shares the entire memory of VM2, which achieves 0 copy > between VMs while being less secure. > 2.1: VM1 and VM2 use an intermediate shared memory to transmit > packets, which results in 1 copy between VMs while being more secure. > > Yes, plan to upstream both. Since the difference is the way to share memory, > I think it wouldn't have too many patches to upstream 2.1 if 2.0 is ready > (or > changing the order if needed). Okay. "Asymmetric" (vhost-pci <-> virtio-pci) and "symmetric" (vhost-pci <-> vhost-pci) mode might be a clearer way to distinguish between the two. Or even "compatibility" mode and "native" mode since existing guests only work in vhost-pci <-> virtio-pci mode. Using version numbers to describe two different modes of operation could be confusing. Stefan
