Comment by newpavlov
2 days ago
>Its capabilities all the way down.
IIUC one problem with such layering of capability processing is that each passed layer results in a context switch (i.e. switch of memory mappings, thrashing of caches, etc.) and its on top of the cost of passing through the kernel. In other words, you may need to pay cost of N syscalls for one multi-layered capability-based operation.
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.