Netflix posted a good article about how to analyze Linux performance issues using the following commands:
uptime dmesg | tail vmstat 1 mpstat -P ALL 1 pidstat 1 iostat -xz 1 free -m sar -n DEV 1 sar -n TCP,ETCP 1 top
For explanation of the output of each command, and what to look for, read the article on Netflix blog here.