Just did a little check and this problem only occurs with the steam controller
xbox 360 controller on USB: no problem
ps3 controller on USB: no problem
steam controller USB wireless receiver (with controller on or off): high cpu use
steam controller connected directly by USB: high cpu use
+1, can confirm, same thing happening on ubuntu 16.04 with latest client
Nothing extracted yet.
Over the last week or so I have noticed that steam is using quite a lot of CPU while idle. htop shows 2 steam processes using ~15% when I have my steam controller USB receiver plugged in. If I unplug the USB receiver the CPU usage immediately drops to ~2%.
This is on slackware-current 64bit
AMD fx-8120 CPU, nvidia gtx560Ti with proprietary drivers.