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    SubjectRe: -rt more realtime scheduling issues
    On Mon, Oct 08, 2007 at 11:04:12PM -0400, Steven Rostedt wrote:
    > On Mon, Oct 08, 2007 at 11:45:23AM -0700, Mike Kravetz wrote:
    > > Are these accurate statements? I'll start working on a reliable delivery
    > > mechanism for RealTime scheduling. But, I just want to make sure that
    > > is really necessary.
    >
    > For i386 I don't think so. Seems that the interrupt handler will set the
    > current task to "need_resched" and on exit of the interrupt handler, the
    > schedule should take place. I don't see the race (that doesn't mean
    > there is one).

    The more I try understand the IPI handling the more confused I get. :(
    At fist I was concerned about an IPI happening in the middle of the
    __schedule routine. But, then it occurred to me that interrupts are
    disabled when in this routine (when holding the runqueue lock). So, IPIs
    are not delivered during __schedule processing. Right?

    But, if this is case then I don't understand the following code in
    schedule():

    local_irq_disable();

    do {
    __schedule();
    } while (unlikely(test_thread_flag(TIF_NEED_RESCHED) ||
    test_thread_flag(TIF_NEED_RESCHED_DELAYED)));

    local_irq_enable();

    How can the reschedule flags possibly be set AFTER running __schedule.
    Especially when the call is explicitly surrounded by local_irq_disable/
    local_irq_enable.

    Can someone help me?
    --
    Mike
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