[time-nuts] FreeBSD, NetBSD, or Minix-III?

Chuck Harris cfharris at erols.com
Sat May 16 15:04:42 UTC 2009


Bob Paddock wrote:
> On Sat, May 16, 2009 at 9:21 AM, Chuck Harris <cfharris at erols.com> wrote:
>> Bob Paddock wrote:
>>
>>> Anyone ever look at Minix-III (Minix-I was the progenitor to Linux)?
>>> Seems like it would be easy to make a decent time server, on
>>> embedded hardware with it.  Past iterations of the Minix-III website
>>> gave a "watch" as an example small embedded system it was meant to
>>> power.
> 
>> Why do you think Minix-III would be a good candidate for a time server?
> 
> Minix-III is based on the microkernel approach of keeping things small and fast.
> Take a look at the web site.  http://www.minix3.org/

I spent an extensive amount of time writing system features for
Minix, back in the day, and even though it was a microkernel,
it was anything but fast.

The good thing about microkernels is they have a very small section
of "trusted" code in the kernel.  Everything else is in user space.
This has nothing to do with speed; it has to do with where the work
gets done.  Ultimately the work has to be done, and that is what causes
bloat and slow operation.  In microkernel systems, the kernel operates
as a task starter, arbiter, allocator of system resources and messaging
system.  Everything is done by passing messages.  The problem with the
microkernel system is your messaging system has to copy tons of data
to do even trivial things.  Another problem is the kernel has to read
the message, interpret what the message means, and check it for validity
before it can do the bidding of the user level task.

In academia, everyone talks of microkernel systems as being the
wave of the future, but in the real world, things end up more in
the monolithic kernel model... linux and BSD are both monolithic
kernels.

>> A "watch" isn't exactly a challenge to an operating system.
> 
> True.  The challenge is putting the OS *in* the Watch,
> as the Embedded System that runs it.

Nobody with any sense would even try.

A watch is such a closed system that it is easy to verify all
parts of it, and there is no need for the frills an OS
provides.

-Chuck Harris



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