David Laight <david@l8s.co.uk> writes:

> Surely you can only do that if you switch out a process running in userspace.
> Most processes are blocked in the bowels of the kernel and have far too much
> kernel state to keep anywhere else.

Read up on what was done in Mach, please. You may want to start here:

http://citeseer.nj.nec.com/draves94control.html

In particular, your statement "too much kernel state to keep anywhere
else" is carefully analyzed, and found to be wrong.

> For threads and LWPs the m-n implementation (presumably) means that threads
> waiting on other threads don't have an LWP.

Yes. The kernel stack consumption is per-LWP (active+blocking-in-kernel
threads), not per thread.

        - Nathan