Virtio-net-multiqueues

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virtio-net Multiqueues provides an approach that scales the network performance as the number of vCPUs increases, by allowing them to transfer packets through more than one virtqueue pair at a time.


Today's high-end servers have more processors, and guests running on them often have an increasing number of vCPUs.


In single queue virtio-net, the scale of the protocol stack in a guest is restricted, as the network performance does not scale as the number of vCPUs increases. Guests cannot transmit or retrieve packets in parallel, as virtio-net has only one TX and RX queue.


Multi-queue support removes these bottlenecks by allowing paralleled packet processing.


Multi-queue virtio-net provides the greatest performance benefit when:


-Traffic packets are relatively large.

-The guest is active on many connections at the same time, with traffic running between guests, guest to host, or guest to an external system.

The number of queues is equal to the number of vCPUs. This is because multi-queue support optimizes RX interrupt affinity and TX queue selection in order to make a specific queue private to a specific vCPU.


NOTE

Multi-queue virtio-net works well for incoming traffic, but can occasionally hurt performance for outgoing traffic.
Enabling multi-queue virtio-net increases the total throughput, and in parallel increases CPU consumption.