About a month ago Anthony Green added a novel “call plan” to libffi . This allows one to cache the hard work of determining what to do once and skip all of that work in subsequent calls. You can read more of the details on their article about it .

The best case for me was about a 25% reduction in amortized overhead for GClosure invocation. In some less ideal situations it was still about a 10% reduction. Not bad!

A merge request for GLib is here , though it will likely require some build system triage since it requires the newest libffi for CI to unblock it.

I also patched libffi to add frame-pointers so I can unwind across ffi boundaries from the Linux perf unwinder. Very handy if you want, you know, to profile your system in a useful manner. And repeated testing here showed about the same (or shockingly less) overhead than the counter-parts. Modern CPU sure are interesting beasts.