Is a multi-user and multi-processor environment useful with threading?

Question

Taking CPU affinity into account, will such an environment be useful with threading? Or will there be a performance degradation in such a system, if multiple users login and spawn multiple kernel and user threads?

Answer 1

When you say "taking CPU affinity into account" - are you saying that all processes have CPU affinity in this hypothetical system? Or is that just as one extra possible bit of information?

Using multiple threads will slow things down a bit if the system is already loaded (so there are more runnable threads than cores) but if there are often times where there are only (say) 2 users and 4 cores available, threading may help.

Another typical use for threads is to do something "in the background" whether that's explicitly using threads or using async calls. At that point multi-threading can definitely give a benefit (e.g. a non-hanging UI) without actually using more than one core simultaneously for much of the time.