In reply to Robin.

We used Siege and Blitz.io. Sieges at 150 concurrent users with the -i flag and a text file full of BP end-point URLs would never complete -- Siege would give up, as HHVM had segfaulted spectacularly.

Blitzes scaling from 1-300 users over a few minutes time would cause it to top out at maybe 175 concurrent users or so and the *BAM* segfault again.

There's no coming back from that, unfortunately -- you have to restart HHVM. PHP-FPM, when under load, will at least come back to some level of functionality as older transactions time out.