How to log CPU usage by processes

You could try to do something like this:

while true; do ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10 >> logfile.txt; printf "\n" >> logfile.txt; sleep 3; done

that would show you the top ten processes in terms of CPU usage. You can change the number of processes shown by changing the 10 in "head -10" to a different number, and how often it updates by changing the 3 in "sleep 3" or taking out the "sleep 3" part entirely.

Most people tend not to watch processor time but instead Processor Queue Length (number of threads waiting for a processor).

That being said there's a good explanation here:

http://www.windowsnetworking.com/articles_tutorials/Key-Performance-Monitor-Counters.html