After upgrading my prosody instance to 0.9.7, it started slowly consuming more and more CPU time. It was already consuming more and more RAM (see #461), so the CPU time consumption is probably not directly related to the memory leak.
As I had to restart it due to CVE-2015-0235, I will have to wait some more weeks before being able to provide hard numbers on which functions are burning the time.
Thanks for the report! I had seen this behaviour on another server too, apparently it's not an isolated case.
I can confirm this issue for two different prosody instances. Both instances use the Debian-Packages of prosody and lua-sec-prosody for debian wheezy.
lua-sec-prosody = 0.5.1-2~wheezy
lua-event = 0.4.3-5~wheezy
storage is internal in both cases.
I forgot to include my munin stats in my confirmation. Here they are.