We started running a setup on hhvm with Flow 3.0, which is mostly hhvm compatible and the performance increase over plain php (even with php-fpm and php7-rc1) was tremendously (talking one order of magnitude).
Other than that, you should put some of the flow caches to some shared memory storage like memcached or APCu (see http://www.michielroos.com/articles/use-memcached-as-your-neos-cache-backend.html).
Well, the possiblities are rather limited without cutting on framework features…:
- try “composer update -o” to create an optimized ClassMap for class loading
- create a special RequestHandler that does a reduced bootstrap and doesn’t initialize parts of the Framework that you don’t need (see Bootstrap::buildRuntimeSequence): Start removing components from the end of the bootstrap sequence (sessions, resources, persistence, reflection, … in that order)
One of the biggest resource wasters is the reflection service, even with all the caching that is already applied, but unfortunately it is a dependency of persistence.