Related:

https://www.usenix.org/system/files/conference/hotos15/hotos...

  We survey measurements of data-parallel systems recently reported in SOSP and OSDI, and find that many systems have either a surprisingly large COST, often hundreds of cores, or simply underperform one thread for all of their reported configurations.

Yes, love that paper.

Anecdotally I have a bit of a track record of 10xing slow systems’ throughout by converting them from distributed to single-node or from multithreaded to single threaded.

Heck I once even sped up a number crunching operation by getting it off of the GPU and onto the vector coprocessor. Because GPUs also have a bunch of extra overhead to have to amortize away.