Main memory bus or cache contention? Integer execution ports full? Throttling? VTune is useful to find out where the bottleneck is, things like that tend to happen when you start loading every logical core.

On Tue, May 5, 2020 at 4:45 PM Joseph Jenne via Python-Dev <python-dev@python.org> wrote:

I'm seeing a drop in performance of both multiprocess and subinterpreter
based runs in the 8-CPU case, where performance drops by about half
despite having enough logical CPUs, while the other cases scale quite
well. Is there some issue with python multiprocessing/subinterpreters on
the same logical core?