Beam Me Through the Datapath: VDUSE for OpenShift Virtualization#

Jakob Meng (Red Hat), Maxime Coquelin (Red Hat)

• Why: Completes a fully-userspace datapath (OVS-DPDK + VDUSE) for KubeVirt VMs, with unusually transparent benchmarking that includes cases where DPDK loses to the kernel datapath.
• What: Extends last year's container userspace work to VMs via VDUSE/vhost-vDPA (primary and secondary networks), plus new workload-partitioning knobs in OpenShift (strict-cpu-reservation, dedicated CPUSet, irqbalanceBanned, static PMD masks). Benchmarks (Xeon Silver 4310, CX-6 Dx, OVS 3.5+): OVS-kernel outperforms OVS-DPDK on large TCP buffers; small-buffer throughput improves with pmd-sleep-max (~90,000 → ~3,000 IRQs/s, QEMU 200% → 115% CPU at 128B buffers) at the cost of large-buffer performance; a virtio-net IRQ-coalescing prototype in the DPDK vhost library fixes that without sleeps. Also documents CX-6 Dx lacking outer-UDP checksum offload (which forced software segmentation — tying into the checksum-offload revamp) and KubeVirt's fixed 256-descriptor virtio rings.
• How: VDUSE is a purely software vDPA device implemented by a userspace application (the OVS DPDK vhost backend), attached through the vDPA bus; vhost-vDPA serves QEMU.
• Where applicable: OpenShift Virtualization, telco and real-time use cases. Preliminary results, explicitly framed as transparent benchmarks; the partitioning APIs are OpenShift-specific but the datapath work is upstream OVS/DPDK.