--lcores: what it does and does not do

[fwefew 4t4tg <7532yahoo@gmail.com>]

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I've made a DPDK test program that does the following on the same machine
and for the same NIC. This is a test; it does nothing practical:

* Creates 1 RX queue then reads and pretty prints contents in a loop
* Creates 1 TX queue then sends packets to a hardcoded IP address in a loop

When I run this program I include the command line arguments
"--lcores=(0)@1,(1)@2" which is passed to 'rte_eal_init'.

This means there's a lcore identified '0' run on CPU HW core 1, and lcore
'1' run on CPU HW core 2.

As I understand it, the intent of the lcores argument is that this test
program will eventually run the RX loop as lcore 0, and the TX loop as
lcore 1 (or vice-versa).

On the other hand after all the required DPDK setup is done --- memzones,
mempools, queues, NIC devices initialized and started --- here's what DPDK
has not done:

* It hasn't started an application thread for lcore 0 or lcore 1
* DPDK doesn't know the function entry point for either loop so no loops
are running.

Which is totally fine ... DPDK isn't magic. If the application programmer
wants a RX and TX application thread pinned to some CPU, it should create
the threads, set the CPU affinity, and run the loop in the NUMA aligned
way. This is trivial to do. That is, with the required DPDK setup done, all
that's left is to do this trivial work ... and the test program is up and
running: problem solved.

The --lcores doesn't and cannot do this application work. So what is the
practical result of it? What does it do?

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