Hayden James has a post on his site sharing a method he's found for getting better performance out of PHP-FPM with the help of a configuration change. In this tutorial he shows how to use the pm static setting to squeeze the best performance out of your web server.

Lets take a very quick look at how best to setup PHP-FPM for high throughput, low latency and a more stable use of CPU and memory. By default, most setups have PHP-FPM’s PM (process manager) string set to dynamic and there’s also the common advice to use ondemand if you suffer from available memory issues.

He starts by defining the three "pm" settings and what they do: dynamic, ondemand and static. He then talks some about how the PHP-FPM process manager is similar to CPUFreq Governor and the settings it allows. Finally he gets into talking about the "pm static" handling, how it relates to available memory and when it makes more sense to use "dynamic" over "static".