CPU affinity of control threads

["Morten Brørup" <mb@smartsharesystems.com>]

Bruce,

I found another gap in the documentation of CPU affinities.

Let's assume a 6-core system.

If a DPDK application is run using:
taskset --cpu-list 0-2 dpdk-app --lcores 3-5

Lcores 3-5 are EAL cores, and each of the three lcores is bound to one cpu, respectively cpu 3, 4 and 5?
Lcore 3 is the main lcore, and lcores 4-5 are worker lcores?
And the original thread of the process (a.k.a. the main lcore) gets its cpuset is changed from 0-2 to 3?

Now, calling rte_thread_create_control() starts a control thread.
Its documentation says:
"Creates a control thread with the given name and attributes. The
affinity of the new thread is based on the CPU affinity retrieved
at the time rte_eal_init() was called, the EAL threads are then
excluded. If setting the name of the thread fails, the error is
ignored and a debug message is logged."

What does that mean?
I.e., what is the affinity of that control thread?

A) Cpu 0-2, controlled by taskset, or
B) cpu 3-5, controlled by the EAL --lcores parameter?


Now, what if the application was run with:
taskset --cpu-list 0-5 dpdk-app --lcores 0-5

Since all cpus are now EAL threads, what happens with rte_thread_create_control() when "the EAL treads are then excluded", and there are no cpus left?


-Morten