php-fpm performance tweaks

https://seniorphp.net/high-performance-apache-with-mpm-event-and-php-fpm/

Next, we edit config file for mpm-event at /etc/apache2/mod-available/mpm-event.conf :

# event MPM
# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestWorkers: maximum number of worker threads
# MaxConnectionsPerChild: maximum number of requests a server process serves 

<IfModule mpm_event_module>
        ServerLimit              256
        StartServers             25
        MinSpareThreads          25
        MaxSpareThreads          75
        ThreadLimit              50
        ThreadsPerChild          25
        MaxRequestWorkers        6400
        MaxConnectionsPerChild   0
</IfModule>