Hi, 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.
For the convenience of discussion, I have some pictures presented at this link: https://github.com/wei-w-wang/vhost-pci-discussion/blob/master/vhost-pci-rfc2.0.pdf Fig. 1 shows the common driver frame that we want use to build the 2.0 and 2.1 design. A TX/RX engine consists of a local ring and an exotic ring. Local ring: 1) allocated by the driver itself; 2) registered with the device (i.e. virtio_add_queue()) Exotic ring: 1) ring memory comes from the outside (of the driver), and exposed to the driver via a BAR MMIO; 2) does not have a registration in the device, so no ioeventfd/irqfd, configuration registers allocated in the device Fig. 2 shows how the driver frame is used to build the 2.0 design. 1) Asymmetric: vhost-pci-net <-> virtio-net 2) VM1 shares the entire memory of VM2, and the exotic rings are the rings from VM2. 3) Performance (in terms of copies between VMs): TX: 0-copy (packets are put to VM2's RX ring directly) RX: 1-copy (the green arrow line in the VM1's RX engine) Fig. 3 shows how the driver frame is used to build the 2.1 design. 1) Symmetric: vhost-pci-net <-> vhost-pci-net 2) Share an intermediate memory, allocated by VM1's vhost-pci device, for data exchange, and the exotic rings are built on the shared memory 3) Performance: TX: 1-copy RX: 1-copy Fig. 4 shows the inter-VM notification path for 2.0 (2.1 is similar). The four eventfds are allocated by virtio-net, and shared with vhost-pci-net: Uses virtio-net's TX/RX kickfd as the vhost-pci-net's RX/TX callfd Uses virtio-net's TX/RX callfd as the vhost-pci-net's RX/TX kickfd Example of how it works: After packets are put into vhost-pci-net's TX, the driver kicks TX, which causes the an interrupt associated with fd3 to be injected to virtio-net The draft code of the 2.0 design is ready, and can be found here: Qemu: https://github.com/wei-w-wang/vhost-pci-device Guest driver: https://github.com/wei-w-wang/vhost-pci-driver We tested the 2.0 implementation using the Spirent packet generator to transmit 64B packets, the results show that the throughput of vhost-pci reaches around 1.8Mpps, which is around two times larger than the legacy OVS+DPDK. Also, vhost-pci shows better scalability than OVS+DPDK. Best, Wei