On Wed, May 31, 2000 at 10:26:31PM +0100, Mark wrote:
> Many thanks for the replies - very helpful. One other thing I want to
> get straight - Which is technically correct (With Respect to the latest
> RT-Linux):
>
> 1) One Process over all with several threads running inside it (Would
> seem the most likely given the POSIX thread concept. Where one is Linux
Yes. Although Linux has its own kernel-threads and user processes and the user
processes
may have POSIX threads inside 'em.
>
> 2) Several processes running on the RTL kernel, where the idle one is
> Linux.
You can think of it this way, if you think of the RTthreads as "processes". The
general convention is that a "process" probably has memory protection and threads
share address space (although this is not always observed) so (1) is more correct.
>
> I just wonder because it seems as though the two are kinda mixed when I
> read documents on RTL.
>
> Thanks and Regards
>
> Mark
>
> In message <[EMAIL PROTECTED]>, Robert Kavaler
> <[EMAIL PROTECTED]> writes
> >I think that RTLinux is better thought of as hierarchical, where the
> >RTLinux scheduler is at the top
> >of the hierarchy, and regular Linux runs as a one process (but of lowest
> >priority) at the next
> >level of the hierarchy. Other processes of higher priority can be added at
> >that level using the RTLinux call pthread_create. The third level of the
> >hierarchy depends on the parent. In the case of Linux, it has
> >its own schedulers in the kernel and of course in user space. It is
> >possible that other RT or non-RT programs have their own subschedulers too.
> >
> >The use of insmod to create RT Tasks is just a convenience. From a memory
> >allocation perspective, RT Tasks are kernel resident so insmod is a great
> >way of loading them into memory. But one of the first
> >things that pthread_create does is go into RTLinux mode (i.e. disables all
> >interrupts) and adds itself to the RTLinux thread list.
> >
> >Here is a picture:
> >
> > RTLinux
> > --------------------------------------
> > | | |
> > Linux Kernel RT Task1 RT Task2 (with sub-scheduler)
> >
> > --------------- ---------------------
> > | | | |
> > Linux Tasks User Tasks Sub Task Sub Task
> >
> >
> >
> >Robert Kavaler
> >
> >
> >Mark wrote:
> >
> >> Hi,
> >>
> >> I'm just trying to figure out how to visualise what going on
> >> when RT-Linux is running. I'm a bit confused trying to figure out how an
> >> RT Linux system fits together.
> >>
> >> For me, with a normal Linux kernel, I think of is running a number of
> >> individual processes. When threads turn up in Linux (VMS or Windoze for
> >> that matter) I think of it as being a separate execution sequence (It
> >> own memory etc.) BUT it is with in a process. That is it can only get a
> >> chance to run when the process is switched into the CPU AND that thread
> >> within the particular process is chosen to execute.
> >>
> >> With RT-Linux is there only ONE process on the system. Is then has a
> >> number of threads inside it (One of which is the Linux Kernel). Then to
> >> start a RTL program off you have to insmod it into the single process?
> >>
> >> I would have a problem if RTL just ran normal processes, where the idle
> >> process was the Linux Kernel. Indeed this is what I though happened,
> >> judging by some of the documents. But the thread stuff seems to
> >> contradict this. Has it been updated in some way.
> >>
> >> Maybe there is a diagram around showing this. As yet I haven't seen on.
> >> On my webpage I've put, what I think is going on. If someone could take
> >> a look and tell me if I way off (Most likely:) of what ever. I'd really
> >> appreciate it.
> >>
> >> http://www.mxnet.demon.co.uk/RT-Linux/RTLinux.html
> >>
> >> Many Thanks
> >>
> >> Mark
> >> -- [rtl] ---
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> >> http://www.rtlinux.org/rtlinux/
> >
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>
> --
> Mark
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