[cbsmith]

The polling loop and I/O interfaces with Vert.x is integrated in to the VM, whereas with Node.js, you'll calling out to libuv/libev/etc. That gives the JVM an advantage. Really, how much actual JavaScript code is V8 JIT'ing at all?

Really what you are comparing here is the efficiency of the paths between the two JavaScript engines and their polling I/O libraries, more than any JIT work (and let's face it, even if we were comparing JIT work, the Sun JVM has had a lot more time to tune and tweak than V8 has). In Node's case, it's talking through libuv, which means it has to transition in-and out of the V8 engine's runtime and in to a C runtime. Even if the C code is super zippy, that's costly. For Vert.x though, all the I/O and polling is integrated in to the runtime/VM/JIT. That's kind of nice.

An interesting way to test what I'm suggesting would be to do the same test with unix domain sockets/named pipes as the transport instead of TCP. The JVM doesn't have a native implementation, so it'd have to call out through JNI. I'd wager even odds it ends up slower than TCP on localhost.