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    SubjectRe: patent on O_ATOMICLOOKUP - Warning actual technical content.
    On Sat, May 25, 2002 at 05:39:00PM -0700, Linus Torvalds wrote:
    > Side note: we could, of course, mark some spinlocks (and thus some
    > code-paths) as being RT-safe, and then make sure that those spinlocks -
    > when they disable interrupts - actually disable the _hw_ interrupts even
    > with the RT patches.
    > That would make those sequences usable even from within a RT subset, but
    > would obviously mean that those spinlocks have to be checked for latency
    > issues - because any user (also non-RT ones) would obviously be truly
    > uninterruptible within these spinlocks.

    How about something more useful: interval progress assurances? Such as
    "during any 5 second period this process will be able to read X meg of
    data from a file and write Y meg"

    So if I have an RT task that dumps data to a DVD at millisecond intervals,
    I can be sure that the non-RT task that reads the FS and puts data
    into a buffer will never let me run out of frames on a given shared memory

    This is useful in itself for nonRT Linux too. It seems quite hard, but it
    could be relatively robust, once it was in place - making a 1 millisecond
    worst case turn into a 10 millisecond worst case would not break it.

    I'm ignoring the 10 billionth rehash of the RTLinux/RTAI debate since
    there seems very little purpose in not doing so. People who have actual
    questions should feel free to ask me directly - publically or privately, I
    don't mind. Those on tape loops can keep repeating themselves without
    my assistance.

    Victor Yodaiken
    Finite State Machine Labs: The RTLinux Company.

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