PHP-FPM / NGINX high CPU load after switch to Debian 7

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http://serverfault.com – I wanted to ask if someone can give me a hint how to identifiy a "high" CPU load problem with an PHP application. We are running our application with PHP-FPM PHP 5.3.27-1~dotdeb.0 and NGINX 1.2.7 on Debian 6 and recently got 5 new application servers. We decided to go with Debian 7, PHP-FPM 5.4.19-1~dotdeb.1 and NGINX 1.4.1 and since then we experience a higher load of on the new servers, which is ~2-5 times higher, sometimes even more, then on the old servers. I've installed PHP5-FPM 5.3 from source on one of the Debian 7 servers, since it's not available from packages anymore, but with no lu (HowTos)