I wrote a little tool for our services that could do basic expression based off of nproc based on an environment variable at startup time.

You could do one thread for every two cores, three threads for every 2 cores, one thread per core ± 1, or both (2n + 1).

Unfortunately the sweet spot based on our memory usage always came out to 1:1, except for a while when we had a memory leak that was surprisingly hard to fix, and we ran n - 1 for about 4 months while a bunch of work and exploratory testing were done. We had to tune in other places to maximize throughput.