netdev - utilizing multi queues of a net device

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Date:   Mon, 2 May 2022 04:29:09 +0000
From:   Eli Cohen <elic@...dia.com>
To:     virtualization <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: utilizing multi queues of a net device

Hi all,

I am experimenting with virtio net device running on a host. The net device has
multiple queues and I am trying to measure the throughput while utilizing all
the queues simultaneously. I am running iperf3 like this:

taskset 0x1 iperf3 -c 7.7.7.24 -p 20000 & \
taskset 0x2 iperf3 -c 7.7.7.24 -p 20001 & \
...
taskset 0x80 iperf3 -c 7.7.7.24 -p 20007

Server instances with matching ports exist.

I was expecting traffic to be distributed over the available send queues but
the vast majority goes to a single queue. I do see a few packets going to other
queues.

Here's what tc qdisc shows:

tc qdisc show dev eth1
qdisc mq 0: root
qdisc fq_codel 0: parent :8 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :7 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :6 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :5 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :4 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :3 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :2 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64
qdisc fq_codel 0: parent :1 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64

Any idea?