Re: replace a legacy proprietary RTOS (Real-Time executive) with NetBSD!

[Antti Kantee <pooka%cs.hut.fi@localhost>]

On Mon Jan 12 2009 at 15:58:01 -0500, Thor Lancelot Simon wrote:
> > What kind of drivers do you have in mind?  I have been thinking
> > about making it possible to run the same device driver code in user-
> > or kernelspace for quite a while now, but I haven't had any motivation
> > apart from "would be nice" so far.  Your goal seems to be a special case
> > of my goal.
> 
> Context-switching to userspace is going to _murder_ performance for
> interrupt driven devices.  The NetBSD kernel is really, really not
> designed to do this with reasonable performance.
> 
> It will be far worse than using a kernel thread as a device interrupt
> handler, which is bad already.  It will probably also perform much
> worse than running many entire applications using separate Xen virtuals,
> with individual virtuals used to provide VM isolation for specific
> device drivers.

Of course it will.  And rm -rf / is an even more effective wide-angle
murder beam.  But just because an option exists doesn't mean you have
to deploy it in your scenario without thinking.