WordPress and high CPU

Hi,

during the last days I’ve installed WordPress and LAMP server on different host (physical and virtual server).

I’m using the latest version of Apache, PHP, MySQL, and WordPress.

Because I’ve to configure and maintain WordPress sites that should have high number of visitors, I do some stress test.

But with just a low number of virtual users (around 120 vu) the WordPress portal give high response time, and the CPU goes to 80-100% (with 1-4 logical CPU).

So I did a simple test. I go to the homepage of a clean WordPress installation (with DEBUG mode off), and just keep pressed F5.
Immediately the CPU goes at high usage percentages, and when I release the F5 button the page show up after a number of seconds proportional to the time I’ve kept pressed the F5 button.

Why WordPress has this behaviour ? What I miss ?
It’s some kind of WordPress or Apache settings that I miss ?

Thank you