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    SubjectRe: RT patch acceptance
    James Bruce wrote:
    > Nick Piggin wrote:
    >
    >> Sorry James, we were talking about hard realtime. Read the thread.
    >
    >
    > hard realtime = mathematically provable maximum latency
    >
    > Yes, you'll want a nanokernel for that, you're right. That's because
    > one has to analyze every line of code, and protect against introduced
    > regressions, which is almost impossible given the pace that Linux-proper

    Thank you, James. Now please tell that to Bill. It would seem
    that I haven't written enough "RT media apps" for him to take
    me seriously ;)

    >
    > If you look at your first two messages in this thread however, you seem
    > to be offering a nanokernel approach (in particular RTAI as suggested by
    > Cristoph) as an alternative to the RT-patch. This is sort of confused
    > by the fact that Ingo called it "hard realtime" because he measured a
    > maximum latency during a stress test. Unfortunately that's not really
    > hard realtime if you are just measuring it; Rather its "really damn good
    > soft realtime". An analysis of code paths could be done to determine if
    > something really does satisfy hard-RT constraints, but to my knowledge
    > that's not on the table at this point. So you're discussing soft
    > realtime if you're dicussing the RT patch.
    >

    No, I clarified the point that the direction the RT people want
    to go in is hard-realtime in the Linux kernel.

    I'm very well aware of what the actual current PREEMPT_RT patch is,
    and I was never talking about that particular patch.

    > So its really just a misunderstanding; Nanokernels certainly still have
    > a place for some applications even with the RT patches applied (Ingo has
    > said as much). However expecting audio applications such as Jack to
    > have to use RTAI is kind of silly, and would end up annoying the authors
    > of both (I'm sure the RTAI people have better things to do than support
    > ALSA drivers in RT mode).
    >

    Yes, Jack is more of a soft realtime application, and in that case
    Linux supports it already today (although perhaps not very well -
    something the RT patch aims to improve).

    [snip rest]

    >
    > I really hope we understand each other now, but if not I guess it wasn't
    > to be. Hopefully someone got something out of reading this discussion,
    > but I won't be posting on this branch of the thread anymore either.
    >

    It seems that you do understand my position now, yes.
    I'll try to refrain from posting further, too.

    Nick

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