Document paralellization options

[martinmodrak]

Write a documentation entry that would describe:

• How we use future for multithreading + link to relevant docs in future
• The cores_per_fit argument
• Some considerations for within-chain paralellization and models running on GPU
  • Within-chain paralellization would usually not be sensible with SBC as there is some overhead to it, while there is almost no overhead for running multiple chains/multiple fits in parallel. So in most cases, assigning one core per chain would result in shorter computation time.
  • Exceptions to the above include:
    • You have a lot of cores and just a few datasets, i.e. you can run all fits and chains at once and still assign multiple cores to single chain
    • You are limited by RAM and thus cannot run too many fits in parallel
  • I have almost no idea how running multiple fits in parallel would interact with GPU paralellization. Most likely one would need to do some trial and error to determine the best configuration (number of workers) for SBC in this setting.