I prevent core 3 (I have 4 cores numbered: 0..3) from being used by anything else on the system by adding isolcpus=3 to my kernel command line parameters.
On reboot this is OK. 'top' shows all 4 cores, with core 3 100% idle. This is as hoped for.

Next I want to run my rust program on core 3 only.
core_affinity::get_core_ids() only returns 3 elements, not 4.
The missing element is for core 3 so I can't then
core_affinity::set_for_current().

This makes it impossible to do what I wanted (run my rust app on its own isolated core).

Does this point to an issue with core_affinity::get_core_ids()? I expected it to return 4 elements.

Thanks for your help. Cheers.