I used to run one of my site (25K unique visitors a day) on PHP 5.3, when HHVM came out with stable version I shifted to HHVM and I had similar experience. Now I am running it on PHP 7 and I have to say I am more than happy with results. As much as PHP is not cool for today's developers it has served on some really high traffic sites and stayed useful even with the test of time.
P.S. Now I wish somebody just implements a good Async IO system and ability to run HTTP right off the PHP engine (I know there is php -S ...; I am talking about a better async system).
This seems interesting hopefully someone will pick this up and make even the mysql_* and other sync functions async too. This could be final nail in the coffin.
We're currently building a pretty large production system in it. It's got a few warts, but it's damned nice, and it's compatibility with ReactPHP (event-loop, not the front-end tool!) is super useful!
You may be looking for React PHP (http://reactphp.org). No relation to the JS library. It is an asynchronous event loop implementation, and there is a native HTTP stack built on top of it.
Can you explain the draw of Async I/O? A single request will not be faster, but you may get more concurrent requests going due to running some while some are waiting for I/O to finish? Is that correct?
When you start talking about multiple concurrent connections, and considering performance of an application as a whole, Async I/O at the application level offers basically no speed benefits over any kind of Sync I/O runtime that can run in parallel.
What an Async I/O model can do is allow the amount of resources consumed by parallel execution contexts to be reduced - therefore allowing you to service more concurrent requests in parallel. But not necessarily any faster, if I/O is your bottleneck in the first place.
It can also be used to give more predictable performance under loads with i.e. response times, if the responses are not dependent on I/O operations to complete.
P.S. Now I wish somebody just implements a good Async IO system and ability to run HTTP right off the PHP engine (I know there is php -S ...; I am talking about a better async system).