On Thu, Mar 23, 2000 at 06:51:42PM +0100, David Olofson wrote:
> Thu, 23 Mar 2000 [EMAIL PROTECTED] wrote:
> > I'm thinking of adding RT schedulable Linux processes that run solely in user
> > space -- when they do a syscall they fall out of RT scheduling.
>
> Have you found a way to replace the normal syscall layer for those threads, or
> similar solution?
This is easy to do via a variety of methods: one is simply to require that the
user links with a special library that uses a second syscall interface and
there are x86 specific methods in which you grab the LDT -- I think this
is what Paolo has done although he should say.
> > They would be memory protected and able to access standard libraries: they
> > would really only be useful for high precision compute tasks and should connect
> > to RT via fifos. Is there much interest in such a feature?
>
> That would be very cool. I don't mind hacking kernel/RTL drivers for the low
> level stuff, but when the major part of the application ends up in kernel
> space (ie needs low latency, hard RT), it starts to get scary...
I'm really interested in such applications because I would like to know
what it is that prevents modularization -- do you really have so much code
that needs hard RT?
>
> Also, I'm still interested in running an audio/DSP engine under RTL (less than
> 2 ms latency, and possibly better SMP performance), and this would eliminate
> the need for running the plugins in kernel space. Would make an excellent RT
> control prototyping tool as well, for those who aren't all that interested in
> audio.
We're looking at alternatives: the new LXRT seems to have some good ideas
in it, there are Ingo's low latency patches, and I've been discussing another
trick somewhat along the LXRT lines. Another possibility is to implement
pseudo-Linux tasks that run in usermode in a special space.
>
> BTW, how do you plan on implementing the FIFOs? Normally, the FIFO read/write
> would be done through kernel calls... Will there be two kinds of kernel calls -
> RT safe and "normal", or will some other interface be used for the FIFOs?
I think that there would be a special trap for FIFO
BTW: the V2.3 has bidirectional fifos in userland.
>
>
> //David
>
>
> P r o f e s s i o n a l L i n u x A u d i o
> · ··-------------------------------------------------·· ·
> MuCoS - http://www.linuxdj.com/mucos
> Audiality - http://www.angelfire.com/or/audiality
> David Olofson - [EMAIL PROTECTED]
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