Perfomance is the speed at which a computer operates in a time. At our company, it is complete a PHP request
Also, scale have same meaning. And i define it as:
Perfomance: Tweak the system to handle most request without upgrade hardware.
Scale: Update hardware to handle more request.
Make a PHP request complete fastest, that's mean we can handle more request in same time.
We can do it very simple, just install google mod_pagespeed (support apache and nginx)
performane increase 2~3x
PHP is interpreted => When we have a request => PHP is combile a code => run it => return.
Solution: Make PHP is compiled
First time have request => PHP combiled source and store to cache, every request later PHP will using binary code from cache.

Reduce PHP combile time 30~60%
Nginx handle static file faster than Apache.
PHP running via FPM
MySQL: Using MariaDB or Pecona
Ex: An Inner join query without condition make Pantheon server die
I'll have a topic about this in next time.
sang@go1.com.au