how to take advantage of all CPUs (only 5x php-fpm processes are running)?

Hello all,

I am new to this forum so I hope I post in the right section.

I am trying to set up a good server for Magento2 using nginx 1.10.0 + PHP 7.0.8 (Zend Engine v3.0.0) on Ubuntu 16.04-64bits. I get good response time when browsing pages already cached by varnish but not when browsing pages that haven't been cached yet. So I disabled the cache feature in Magento2 and I made stress tests with http://www.magespeedtest.com (which uses siege, see https://www.joedog.org/siege-home/).

Using the command htop, I realized 5x php-fpm processes were hitting hard on 5x different CPU. But if I install the same configuration on a 32 cores VPS, I still get only 5x processes (thus leaving 27x CPUs unused).

I tried to change "worker_processes 25" instead of "worker_processes auto" in /etc/nginx/nginx.conf but it didn't change anything

How can I take advantage of the 32x CPUs?

Thanks for any help

macsym