@kumaraditya303 just published a post on the Quansight blog I thought might be of interest here. It summarizes work he led and I helped out on to improve multithreaded scaling of NumPy. I suspect there will be a lot of debugging stories like this across the ecosystem to chase down scaling bottlenecks under threads so I hope the anecdotes and explanations of all the different bottlenecks we ran into are helpful.
https://labs.quansight.org/blog/scaling-numpy-on-free-threaded-python