PHP saturation after upgrade from 2.1.0 to 2.2.:X0 (4 replies)

Hi, I just upgraded Piwik from 2.1.0 to 2.2.0.
Everything was working fine before upgrade but after, the CPU stays at 100% (7% before upgrade, on a heavy traffic website).

I'm running it on Debian Wheezy, Nginx and php 5.5 and Piwik is totally innaccessible !

php fpm log says :
[17-Apr-2014 17:03:03] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 32 children, there are 0 idle, and 49 total children

Thanks for your help