OK. Finally I got it.
There is not good distribution of rx queues between pmd
threads for dpdk0 port.
> # ./ovs/utilities/ovs-appctl dpif-netdev/pmd-rxq-show
> pmd thread numa_id 0 core_id 13:
> port: vhost-user1 queue-id: 1
> port: dpdk0 queue-id: 3
> pmd thread numa_id 0 core_id 14:
> port: vhost-user1 queue-id: 2
> pmd thread numa_id 0 core_id 16:
> port: dpdk0 queue-id: 0
> pmd thread numa_id 0 core_id 17:
> port: dpdk0 queue-id: 1
> pmd thread numa_id 0 core_id 12:
> port: vhost-user1 queue-id: 0
> port: dpdk0 queue-id: 2
> pmd thread numa_id 0 core_id 15:
> port: vhost-user1 queue-id: 3
> ------------------------------------------------------
As we can see above dpdk0 port polled by threads on cores:
12, 13, 16 and 17.
By design of dpif-netdev, there is only one TX queue-id assigned
to each pmd thread. This queue-id's are sequential similar to
core-id's. And thread will send packets to queue with exact this
queue-id regardless of port.
In our case:
pmd thread on core 12 will send packets to tx queue 0
pmd thread on core 13 will send packets to tx queue 1
...
pmd thread on core 17 will send packets to tx queue 5
So, for dpdk0 port:
core 12 --> TX queue-id 0
core 13 --> TX queue-id 1
core 16 --> TX queue-id 4
core 17 --> TX queue-id 5
After truncating in netdev-dpdk:
core 12 --> TX queue-id 0 % 4 == 0
core 13 --> TX queue-id 1 % 4 == 1
core 16 --> TX queue-id 4 % 4 == 0
core 17 --> TX queue-id 5 % 4 == 1
As a result only 2 queues used.
This is not a good behaviour. Thanks for reporting.
I'll try to fix rx queue distribution in dpif-netdev.
Best regards, Ilya Maximets.
P.S. There will be no packet loss on low speeds. Only 2x
performance drop.
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