[Freeswitch-users] Number of CPU

Hi guys, I am using the master version from couple of months ago. I started running it on an 8 CPU AWS instance on Ubuntu 14. It seems that FS is only using the first 4 CPUs. The load on the other 4 is consistently much lower and we started getting voice quality issues at about the same number of concurrent calls as a 4 CPU instance. Is this a known issue or am I imagining things?