Upgrade postgresql from 9.1 to 9.6

I am trying to upgrade my postgresql database from version 9.1 to 9.6 using pg_upgrade utility. 

I have started this activity with 6 threads and running with no issues but I can see only 2 active threads of pg_upgrade  when checked on OS using "ps -ef| grep pg_upgrade" which might slow down my upgrade process. 

Is there any limit of adding jobs in "-j" parameter in pg_upgrade utility? 

Or is there any settings that I need to configure in postgresql.conf file? 

Below are the configuration of my server:

OS : Amazon Linux

RAM: 64GB

CPU: 16

DB size : 5 TB

Upgrade utility : pg_upgrade 

Jobs: 6

Issue : only 2 threads of pg_upgrade are active

Appreciate your help!! 

Thanks, 

Sohel