Simon Farnsworth (simon.delete@this.farnz.org.uk) on March 15, 2021 3:12 am wrote:
> anon2 (anon.delete@this.anon.com) on March 15, 2021 1:58 am wrote:
> > Anon (no.delete@this.spam.com) on March 14, 2021 11:49 pm wrote:
> > > Linus Torvalds (torvalds.delete@this.linux-foundation.org) on March 14, 2021 4:58 pm wrote:
> > > > That kind of thing could be useful for a microkernel (not that I believe in the
> > > > concept - I continue to be of the opinion that microkernel proponents are overplaying the advantages,
> > > > and underplaying the very real issues with communication and sharing).
> > >
> > > In several places I saw Linux being classified as "microkernel", I never touhgt
> > > this classification have any relevance, but now I read you bashing the concept.
> > >
> > > So, is Linux a microkernel after all?
> >
> > No. It has taken some concepts and applied them where they are are a good fit
> > (e.g., to implement userspace device drivers for certain classes of device).
> >
> > > What is the true concept of microkernel?
> > >
> >
> > Traditionally it is a minimal kernel that supports only thread scheduling, low level interrupt handling,
> > IPC, and perhaps low level virtual memory management. The
> > rest of the kernel services are built with threads
> > (which may or may not be in different address spaces and privilege modes) on top of that base.
> >
> > It sounds like such a nice clean idea that even experienced computer scientists
> > and engineers throw away careers trying to make it work like a monolithic kernel.
> > The reality is not all problems can be decomposed into "clean, simple".
> >
> It also promises a route to extreme stability; the core kernel does IRQ handling, a simple form of
> IPC, address spaces and task switching (noting that it's up to the user of these facilities to pair
> tasks with address spaces), and nothing else, and hence in theory can be made completely bug free.

In theory so can the core of a monolithic kernel.

>
> Then, whenever another component of the system fails, you "merely" have to kill and restart
> it to return to normal operation - if everything is built to handle crashes, then this Just
> Works. In practice, life is not that simple, and designing your tasks to handle a crash and
> restart cleanly is also a hard problem, especially in the face of real hardware behaviour.

Killing and restarting things is haphazard and no vast improvement to stability.