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authorSteven Luong <sluong@cisco.com>2020-03-23 09:34:59 -0700
committerSteven Luong <sluong@cisco.com>2020-04-27 09:25:32 -0700
commitbc0d9ff6727d77668e216aba1c6d6cb753fa2ac3 (patch)
treedc2af469cf255d3d819dd52f1cc6703d708f9728 /docs
parentba6deb96e923f71aa9387c06000412c3fb1362fa (diff)
virtio: support virtio 1.1 packed ring in vhost
virtio 1.1 defines a number of new features. Packed ring is among the most notable and important one. It combines used, available, and descripptor rings into one. This patch provides experimental support for packed ring. To avoid regression, when packed ring is configured for the interface, it is branched to a separate RX and TX driver. Non packed ring should continue to perform as it was before. Packed ring is tested using qemu4.2 and ubuntu focal fossa (kernel 5.4.0-12) on the guess VM which supports packed ring. To configure VPP with packed ring, just add the optional keyword "packed" when creating the vhost interface. To bring up the guest VM with packed ring, add "packed=on" in the qemu launch command. To facilitate troubleshooting, also added "verbose" option in show vhost desc CLI to include displaying the indirect descriptors. Known qemu reconnect issue - If VPP is restarted, guest VMs also need to be restarted. The problem is kernel virtio-net-pci keeps track of the previous available and used indices. For virtio 1.0, these indices are in shared memory and qemu can easily copy them to pass to the backend for reconnect. For virio 1.1, these indices are no longer in shared memory. Qemu needs a new mechanism to retrieve them and it is not currently implemented. So when the protocol reconnects, qemu does not have the correct available and used indices to pass to the backend. As a result, after the reconnect, virtio-net-pci is reading the TX ring from the wrong position in the ring, not the same position which the backend is writing. Similar problem exists also in the RX. Type: feature Signed-off-by: Steven Luong <sluong@cisco.com> Change-Id: I5afc50b0bafab5a1de7a6dd10f399db3fafd144c
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