Re: RT patch acceptance

Paul E. McKenney
2005-06-01T02:43:33Z

On Tue, May 31, 2005 at 09:14:59PM -0400, Karim Yaghmour wrote:
>
> [ removed a lot of interesting stuff ... ]
>
> Andrea Arcangeli wrote:
> > The point where preempt-RT enters the hard-RT equation, is only if you need
> > syscall execution in realtime (like audio, but audio doesn't need
> > hard-RT, so preempt-RT can only do good from an audio standpoint, it
> > makes perfect sense that jack is used as argument for preempt-RT). If
> > you need syscalls with hard-RT, the whole thing gets an order of
> > magnitude more complicated and software becomes involved anyways, so
> > then one can just hope that preempt-RT will get everything right and
> > that somebody will demonstrate it.
>
> Please have a look at RTAI-fusion. It provides deterministic
> replacements for rt-able syscalls _transparently_ to STANDARD
> Linux applications. For example, an unmodified Linux application
> can get a deterministic nanosleep() via RTAI-fusion. The way
> this works, is that rtai-fusion catches the syscalls prior to
> them reaching Linux. So even the syscall thing isn't really a
> limitation for RTAI anymore.

I -completely- misinterpreted

http://www.fdn.fr/~brouchou/rtai/rtai-doc-prj/rtai-fusion.html

on first reading some months ago. It looks much more interesting
on second reading. It does not have the degree of isolation that
the pure double-kernel approaches do, since as the paper states,
Linux can "hide" tasks that are waking up from I/O events.
However, it does appear to provide a unified user-level environment.

I will add it to my list of approaches to realtime in Linux!

Thanx, Paul

> Philippe would be in a better position to elaborate, but that's
> the essentials of it.
>
> Karim
> --
> Author, Speaker, Developer, Consultant
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