You are running a tail -f in an iTerm tab for a busy log file. Did you know that this could use quite a bit of CPU? In one case I had today, iTerm was using more than 30% of the CPU. This looks like a bug. Luckily, there is an easy workaround: minimize the iTerm window by clicking on the orange "-" button and iTerm's CPU usage will drop down to no more than couple of percents.