We have just completed an update of PHP on our servers. We went from 5.3 to 5.5. We have a pretty big site with lots of nodes, blocks, views, modules and users. Everything was working "ok" (there are some area's we know we can improve) but now with php 5.5 our response time has almost tripled on our main Drupal 7 instalation. On other Drupal 7 instalation the response times went down.
Digging more in to this we found that there were 3 hooks that really caused this increase:
We are using all the goodies to increase our performance: PHP runs in FPM, we have memcache, varnish, PHP OPcache.
Has anyone else had some problems with using PHP 5.5 for a large site?