The kdbuswreck

I realize that a dbus-like design (central daemon relaying messages) will probably take a performance hit due to context switches and copies. However, there's no reason that a synchronous method call should need 15 context switches, nor is there any reason that dbus couldn't use memfd for large messages.

Regardless, this particular dbus benchmark is so incredibly slow that none of this explains it, and kdbus is apparently only twice as fast. I'm not sure what the problem is, but it's not the scheduler or the fact that there's a central daemon.

IOW, yes, kdbus is in principle twice as fast as a dbus-like design. But dbus is several hundred times slower than it should be. Let's fix that first before quibbling over the other factor of two by moving some or all of it into the kernel.