> All of the memory you describe for other purposes is allocated at user level and booked to processes.
No, they aren't. A microkernel is responsibe for basic thread management and IPC. Both of which are highly dynamic in nature.
You seem to be confusing the system that decides when to make a scheduling decision (userspace process - although still part of the microkernel project, so still included in all this anyway), with the system that actually executes that decision (the microkernel itself). And in the case of systems like QNX the kernel will even do its own decisions independent of the scheduler service, such as switching the active thread on MsgSend.
But whether or not it's in ring0 or ring3 is independent of whether or not it's part of a microkernel. A microkernel delegates responsibility to ring3 processes, but those processes are part of the microkernel system - they are in fact a very critical aspect of any microkernel project, as without them you end up building a bootloader with aspirations of something bigger than a kernel.
> A microkernel delegates responsibility to ring3 processes, but those processes are part of the microkernel system
I disagree. Certainly you won't get a usable system without some core services, but the fact that you can replace these services with your own as long as you satisfy the protocol means there's a strong isolation boundary separating them from the kernel. Certainly they are essential components of the OS, just not the kernel.
As for the alleged dynamism of thread management and IPC, I don't see how it's relevant. There exist asynchronous/non-blocking IPC microkernel designs like VSTa and Minix in which the kernel allocates and manages storage for asynchronous message sends, but it's long since proven that such designs are hopelessly insecure. At the very least, it's trivial to DoS such a system.
Only bounded message sends with send/receive buffers provided by processes can you avoid this inevitability. If the idea with Fuchsia is to reimagine consumer operating systems, avoiding the same old mistakes seems like a good idea.
As for scheduling, that's typically part of the kernel logic, not a user space process. Yes, message sends can donate time slices/migrate threads, but there are priority inversion problems if you don't do this right, as L4 found out and avoided in the seL4 redesign. I honestly don't know why Google just didn't use or acquire seL4 for Fuchsia.
No, they aren't. A microkernel is responsibe for basic thread management and IPC. Both of which are highly dynamic in nature.
You seem to be confusing the system that decides when to make a scheduling decision (userspace process - although still part of the microkernel project, so still included in all this anyway), with the system that actually executes that decision (the microkernel itself). And in the case of systems like QNX the kernel will even do its own decisions independent of the scheduler service, such as switching the active thread on MsgSend.
But whether or not it's in ring0 or ring3 is independent of whether or not it's part of a microkernel. A microkernel delegates responsibility to ring3 processes, but those processes are part of the microkernel system - they are in fact a very critical aspect of any microkernel project, as without them you end up building a bootloader with aspirations of something bigger than a kernel.