CPU 16 cores 14 GB RAM Apache 2.2.16 PHP 5.3.3-7 with enabled APC
Apache mpm config:
StartServers 50 MinSpareServers 50 MaxSpareServers 256 MaxClients 256 MaxRequestsPerChild 0
With about 20-30 simultaneous connections apache requests take a lot of time, because CPU raised to 100%
mod_stat shows RANDOMLY apache processes and random scripts, that use more than 5% cpu
php applications worked greate with smaller hardware configuration and ths situation seems strange.