Comment by Agingcoder

Yes exactly.

The kernel tries to guess as well as it can though - many years ago I hit a fun bug in the kernel scheduler that was triggered by numa process migration ie the kernel would move the processes to the core closest to the ram. It happened that in some cases the migrated processes never got scheduled and got stuck forever.

Disabling numa migration removed the problem. I figured out the issue because of the excellent ‘a decade of wasted cores’ paper which essentially said that on ‘big’ machines like ours funky things could happen scheduling wise so started looking at scheduling settings .

The main numa-pinning performance issue I was describing was different though, and like you said came from us needing to change the way the code was written to account for the distance to ram stick. Modern servers will usually let you choose from fully managed ( hope and pray , single zone ) to many zones, and the depending on what you’ve chosen to expose, use it in your code. As always, benchmark benchmarks.