Comment 5 for bug 1668829

The proposal to work around the problem by using multiple vhost-user queues per port cannot solve the problem as it has two prerequisites that are not generally fulfilled:

1. The guest application needs to be able to use multiple queues and spread its Tx traffic across them.
2. The OpenStack environment must support configuration of vhost multi-queue.

The work-around to increase the queue length to 1024, in contrast, is completely transparent for applications and reduces the likelihood of packet drops for all types of sub-ms scale load fluctuations, no matter their cause.

In general we believe that it would be good to dimension the virtio queue size roughly equal to the typical queue sizes of physical interfaces (typically ~1K packets) to avoid that the virtio queues are the weakest link in the end-to-end data path.

To this end we do support the idea of making the virtio-net queue size configurable in both directions (Rx and Tx) in upstream Qemu.