RE: Followup British Telecom outage reason

[Vadim Antonov <avg () exigengroup com>]

Realtime stuff is not only about process rescheduling times.

The definition of real-time system is: a system which can guarantee
execution of tasks within specified time limits.

I've seen a real-life real-time system with guaranteed reaction time of
two hours (it was controlling irrigation water gates).

For routers, the "real-time" limits one needs is in 0.1 second-range;
making a system like that from a general-purpose OS is certainly doable.

--vadim

On Thu, 29 Nov 2001, Joel Jaeggli wrote:

> Um... The rtl kerenel runs the linux kernel as a pre-ementible low
> priority thread, has proveable worst case timing around 15uSec between
> assertion of interrupt and execution of the realtime handler, and is 
> posix compliant.
>
> visit:
>
> http://www.rtlinux.org/
>
> and
>
> http://www.fsmlabs.com/
>
>
>
>
> On Thu, 29 Nov 2001, Youse, Chuck wrote:
>
> > You'll forgive me for being cynical here, but I seriously doubt that any
> > Linux-derived operating systems could truly qualify as 'real-time'.  To meet
> > the requirements for an RTOS, Linux would have to be so heavily mutated that
> > it would no longer be Linux.
> >
> > Cheers
> > Chuck
> >
> > -----Original Message-----
> > From: Patrick Greenwell
> > To: Christian Kuhtz
> > Cc: Alex Bligh; Paul Vixie; nanog () merit edu
> > Sent: 29/11/01 07:49
> > Subject: RE: Followup British Telecom outage reason
> >
> >
> > On Wed, 28 Nov 2001, Christian Kuhtz wrote:
> >
> > > > I guess some time someone will realize routers are both
> > > > hardware, and software, and shock horror both, if done
> > > > well, can actually add value. [hint & example: compare the
> > > > scheduler on, say, Linux/FreeBSD, Windows 95 (sic),
> > > > and your favourite router OS (*); pay particular attention
> > > > to suitability for running realtime, or near realtime tasks,
> > > > where such tasks may occasionally crash or overrun their
> > > > expected timeslice; note how the best OS amongst the
> > > > bunch for this aint exactly great].
> > > >
> > > > (*) results may vary according to personal choice here.
> > >
> > > Don't use a non-realtime OS for something that you expect realtime or
> > > near-realtime OS functionality.  There are specific systems to address
> > these
> > > kinds of needs with rather complicated scheduling mechanism to
> > accomodate
> > > such requirements in a sensible manner.
> > >
> > > Is IOS a realtime operating system?  No.  Are any of the other listed
> > OS
> > > realtime operating systems?  No.
> >
> > Actually there are multiple Linux-based RTOSes.
>
> -- 
> -------------------------------------------------------------------------- 
> Joel Jaeggli                                 joelja () darkwing uoregon edu    
> Academic User Services                             consult () gladstone uoregon edu
>      PGP Key Fingerprint: 1DE9 8FCA 51FB 4195 B42A 9C32 A30D 121E
> --------------------------------------------------------------------------
> It is clear that the arm of criticism cannot replace the criticism of
> arms.  Karl Marx -- Introduction to the critique of Hegel's Philosophy of
> the right, 1843.