True, but capability calls in SeL4 are supposedly faster than linux syscalls. Because caps are such an important primitive, they're extremely heavily optimised.

As an example, when you invoke a capability, your process hands the callee your scheduler time-slice. So its not like linux where your process yields to the scheduler. The same CPU core will handle the entire call -> process -> return computation pipeline between multiple processes.

I'm not sure how fast it ends up in practice compared to a similar system built on top of linux. I suspect a lot of the difference would come down to implementation choices. And if its still not fast enough, you can always just set up a ring buffer or something between processes to share data directly.