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    SubjectShielded CPUs

    This might be a bit off-topic (and might belong in the rtlinux mailing
    list), but I wanted people's opinion on LKML...

    There's an article in the May 2004 Linux Journal about some CPU affinity
    features in Redhawk Linux that allow a process and a set of interrupts to
    be locked to a particular CPU for the purposes of improving real-time
    performance. This technique is dubbed CPU Shielding
    ( and the claim is made
    that a user program that is thus configured (with the appropriately
    patched kernel, of course) can acheive deterministic (hard) real-time
    performance. The author claimed you can get (bounded) interrupt response
    time in the 100s of microseconds, and he alluded to the fact that
    scheduling jitter also is reduced and bounded with a hard limit.

    Does this make any sense to anyone here?

    Specifically, what about, among other things, priority inversion?

    Presumably your high priority task is always undergoing some small amount
    of priority inversion if it touches a spinlock. Worse yet, if your
    process ever has to touch anything in the Linux kernel that needs to sleep
    (such as, say, memory being swapped from disk) then your hard realtime
    program has just failed to be hard realtime.

    Does anyone know anything more about this? Is this magic?! The author of
    this paper certainly makes it seem like it is...

    Perplexedly yours,


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