One of our customers has an issue where our load average on two of the boxes spikes on peak loads. What I got from testing is consistent with what they were reporting: on CentOS 7, the load spikes in hockey stick fashion, from 40-50% up to 200%, with very high iowait values. On CentOS 6, load increases and decreases linearly and the machine never slows down.
Asterisk version is 188.8.131.52, which is if course quite old (but it is what is installed). The CentOS 6 box actually has less RAM (8 Gb vs. 16 Gb), but other than that they are exactly identical in hardware configuration.
I checked the usual culprits, but to no avail. Is this a known issue?