Last week we noticed that the default scheduler isn’t being set properly in CentOS 7. I haven’t checked this for CentOS 6, but it might be worth exploring.
The TL;DR is unless you’re running CentOS 7 on a laptop or as a virtual guest, you should probably run
'tuned-adm profile throughput-performance'
I wrote up the full details here -> http://jperrin.org/CentOS/boosting-CentOS-server-performance/