parallel processing – How to measure performance of Node.js service?

There is a service Node.js that makes a useful calculations. It is index.js file.

There is a queue of events. Another service reads these events and calls the first service.

I wonder should I call node.js services separately like:

event1 -> node index.js
event2 -< node index.js

Or run one node process and inside listen events and handle them:

run node.js
   event1 -> handle
   event2 -> handle

Or the third way:

run node.js (process 1)
   event1 -> handle
   event2 -> handle

run node.js (process 2)
   event1 -> handle
   event2 -> handle

How to measure performance in this case and make a right decision?