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    SubjectRe: Minutes from Feb 21 LSE Call
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    On Tue, Feb 25, 2003 at 03:30:59PM +0000, Alan Cox wrote:
    > Nothing is conceptually obvious. Thats the difference between 'science'
    > and engineering. Our bridges have to stay up.

    Yes, I absolutely agree with this. It shouldn't be the case where one is
    over the other, they should have a complementary relationship.

    > > It's about getting relationship inside the kernel to respect and be
    > > controllable by the scheduler in some formal manner, not some random
    > > not-so-well-though-out hack of the day.
    >
    > Prove it, compute the bounded RT worst case. You can't do it. Linux, NT,
    > VMS and so on are all basically "armwaved real time". Now for a lot of
    > things armwaved realtime is ok, one 'click' an hour on a phone call
    > from a DSP load miss isnt a big deal. Just don't try the same with
    > precision heavy machinery.
    >
    > Its not a lack of competence, we genuinely don't yet have the understanding
    > in computing to solve some of the problems people are content to armwave
    > about.
    >
    > If I need extremely high provable precision, Victor's approach is right, if
    > I want armwaved realtimeish behaviour with a more convenient way of working
    > then Victor's approach may not be the best.

    I spoke to some folks related to CMU's RTOS group about a year ago and was
    influenced by their preemption design in that they claimed to get tight RT
    latency characteristics by what seems like some mild changes to the Linux
    kernel. I recently start to investigate their stuff, took a clue from them
    and became convince that this approach was very neat and elegant. MontaVista
    apparently uses this approach over other groups that run Linux as a thread
    in another RT kernel. Whether this, static analysis tools doing rate{deadline}-monotonic
    analysis and scheduler "reservations" (born from that RT theory I believe)
    are unclear to me at this moment. I just find this particular track neat
    and reminiscent of some FreeBSD ideals that I'd like to see fully working in
    an open source kernel.

    Top level link to many papers:
    http://linuxdevices.com/articles/AT6476691775.html

    A paper I've take interest in recently from the top-level link:
    http://www.linuxdevices.com/articles/AT6078481804.html

    People I originally talked to that influence my view on this:
    http://www-2.cs.cmu.edu/~rajkumar/linux-rk.html

    > Its called engineering. There are multiple ways to build most things, each
    > with different advantages, there are multiple ways to model it each with
    > more accuracy in some areas. Knowing how to use the right tool is a lot
    > more important than having some religion about it.

    Yes, I agree. I'm not trying to make a religious assertion and I don't
    function that way. I just want things to work smoother and explore some
    interesting ideas that I think eventually will be highly relevant to a
    very broad embedded arena.

    bill

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