I had a problem with my VPS like a week ago, and I had to completely reinstall it for it to work. It worked, but just for a while.
Everything was alright until now, I really don't know what the problem is.
The mysql error log has errors about
maxrequestworkers, so we increased the max workers, but that didn't do anything, still at 100%.
I'm attaching an image of top so you can see what's doing it:
btw, im on DEBIAN 8.
There is screen without mysql process, just check screenshot.
MYSQL TUNER SCREENSHOT.