Is there a way to "throttle" MacPorts? I have an unusual request. 

I'd like to slow down MacPorts. It sometimes uses a ton of CPU resources, and rather than having it run at full speed, I'd like it to run slowly and in the background. 

So, instead of it compiling things in parallel (e.g. four instances of clang, each at >80% CPU usage according to top), I'd like it to use at most N cores, or perhaps some maximum total percentage of the CPU. 

Obviously running in serial and/or throttled means it would take longer to complete. I'm okay with that. I'm looking for some extra control for special circumstances. 

The benefits of this behavior include more computer resources devoted to whatever else I'm doing and not heating up my old laptop too much. :-)
You can set the number of cores used by updating buildmakejobs in the macports.conf file.  By default all cores are used. 


  buildmakejobs
  
  Number of simultaneous make jobs (commands) to use when building ports. Using “0” will cause a runtime autodetection to use all available processor cores.
  
  Default: 0


This file is in ${prefix}/etc/macports where ${prefix} default is /opt/local