Understand what is using up "nice" CPU
I am running a small Cassandra cluster on Google Compute Engine. From our CPU graphs (as reported by collectd), I notice that a nontrivial amount of processor time is spent in NICE. How can I find out what process is consuming this? I've tried just start top and staring at it for a while, but the NICE cpu usage is a bit spikey (most of the time, NICE is at 0%; only on occasion will it spike up to 30-40%) so "sit and wait" isn't very effective.
Answer
"Nice" generally refers to to the priority of a process. (More positive values are lower priority, more negative values are higher priority.) You can run ps -eo nice,pid,args | grep '^\s*[1-9]' to get a list of positive nice (low priority) commands.
On a CPU graph NICE time is time spent running processes with positive nice value (ie low priority). This means that it is consuming CPU, but will give up that CPU time for most other processes. Any USER CPU time for one of the processes listed in the above ps command will show up as NICE.