Re: Microkernel architecture?

[Gary Thorpe <gathorpe79@xxxxxxxxx>]

 --- David Leimbach <leimy2k@xxxxxxx> wrote: > 
> On Oct 8, 2003, at 12:22 AM, Gary Thorpe wrote:
> 
> > Yeah, an exokernel sounds cool...until you realize that every
> single  
> > application needs to be linked into libraries that implement an OS 
> 
> > basically. What does that do for memory usage? How protected is the
>  
> > machine from malicious/errant applications? Security? IPC?
> >
> 
> Different strokes for different folks.  Some embedded systems only
> need  
> to run 1 application ever.  So none of the above matters.
> 
> OS doesn't mean one thing to all people... nor should it.

Why not just use a modified version of DOS with everything built into
the application itself? Same result isn't it? Why have an exokernel at
all--if almost all the OS functionality is built into each application,
then it won't be much harder to build it all in. There is nothing
particularly new or innovative with this idea.

> 
> > A microkernel makes it possible to modularize the OS, but an
> exokernel  
> > sounds like it forces all the applications to be monolithic OS+app 
> 
> > hybrids. The speed comparisons on the ExOS web site don't even use
> a  
> > particularly fast web server for BSD (or is NCSA now considered
> high  
> > performance as well as obsolete?).
> 
> Yeah its like an embedded executive.  The whole focus is that you
> want  
> the application to get all the resources it needs to do its job
> as fast as possible.  At least that's always been my understanding.
> 
> Microkernels are a step in the opposite direction from that.

You should be more accurate: the microkernel design is not intended to
_slow_ things down, just seperate things (which on many architectures
mean they must slow down). My point in mentioning their benchmarks is
that they did not do a realistic comparison of an exokernel to a
monolithic system as no one uses the NCSA web server pratically. If it
really is super fast, then compare it to the best you can get on a BSD
system or Linux.

> 
> >
> > Pedro Giffuni wrote:
> >
> >> This is off topic, (but just for reference and because there is
> not
> >> technical-chat list ...)
> >> when you mentioned you wanted a userland VFS API, I recalled
> someone  
> >> already did
> >> that: in fact, they turned everything into libraries and made the 
> 
> >> kernel very
> >> small... they called it an Exokernel:
> >> http://www.pdos.lcs.mit.edu/exo.html
> >> They invented softupdates, BTW :).
> >
> >
> > I believe Sun funding some research into improving FFS and the  
> > resultant code first emerged on BSD:
> > http://www.netbsd.org/Documentation/tune/5.html#a3
> > http://www.netbsd.org/Documentation/misc/#softdeps
> > http://www.mckusick.com/softdep/index.html
> > http://www.usenix.org/publications/library/proceedings/usenix99/ 
> > mckusick.html
> >
> > No mention of exokernels...was it used for the development?
> >
> >> cheers,
> >>     Pedro.
> >
>  

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