What makes Apache slow to render simple html?

Question

Apache HTTP Server

Server version: Apache/2.4.6 (CentOS).
2 SSD drives Raid1, free 75% of the drive.
CPU 4 cores, 8 threads.
Apache is configured by default, MPM is prefork.
LoadAverage does not exceed 0.5-0.7 in all respects.
Before the swap as before the star.
Disk operations in kilobytes / s, no process seriously loads the system.
Periodically, once a day, at any time of the day, there are freezes in the return of pages. Moreover, the simplest html file with a small text is used for verification.
By default, the delay time until the page is received is ~ 70 ms, and then jumps up to 500 ms, 1-2 seconds, begin!
At this point, httpd processes are usually somewhere around 55-100, the processor is not loaded at all, there are no network problems ... but httpd periodically gives such a wild delay.
It can last from 5 minutes to several hours, and somehow unstable, not every second.
According to netstat, there are no extra connections.
Already scratched my head what could be the problem. I'm starting to sin on the SSD. True, I don’t know how to check the influence of the disk on this.

Answer 1

I lied a little, MPM is not workers, but prefork.