KVM VMs vhost-user

FD.io CSIT performance lab is testing VPP vhost with KVM VMs using following environment settings:

• Tests with varying Qemu virtio queue (a.k.a. vring) sizes: [vr1024] 1024 descriptors to optimize for packet throughput.
• Tests with varying Linux CFS settings: [cfs] default settings, [cfsrr1] CFS RoundRobin(1) policy applied to all data plane threads handling test packet path including all VPP worker threads and all Qemu testpmd poll-mode threads.
• Resulting test cases are all combinations with [vr1024] and [cfs,cfsrr1] settings.
• Adjusted Linux kernel CFS scheduler policy for data plane threads used in CSIT is documented in CSIT Performance Environment Tuning wiki.
• The purpose is to verify performance impact (MRR and NDR/PDR throughput) and same test measurements repeatability, by making VPP and VM data plane threads less susceptible to other Linux OS system tasks hijacking CPU cores running those data plane threads.