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    SubjectRe: Real-Time Preemption, -RT-2.6.12-final-V0.7.50-24

    * Karsten Wiese <annabellesgarden@yahoo.de> wrote:

    > looked at -50-33 now and wonder why is mask_IO_APIC_irq() called twice
    > from __do_IRQ()? given a threaded interrupt: __do_IRQ() calls
    > desc->handler->ack(irq). ack points to
    > mask_and_ack_level_ioapic_irq(), which calls mask_IO_APIC_irq(irq).
    > some lines later in __do_IRQ() desc->handler->disable(irq) is called.
    > disable points to mask_IO_APIC_irq(), now being called a 2nd time. I
    > think this 2nd call isn't necessary. Is there a difference between
    > masking an interrupt line and disabling it? What am I missing?

    you are not missing anything - but i found no easy way for the time
    being to get rid of the second masking.

    > Back at 2.6.12-rc5-RT-48-16 mask_and_ack_level_ioapic_irq() also
    > contained the mask_IO_APIC_irq(irq) call and level interrupt-rates
    > where fine. Some versions later it vanished there. Why was that?

    i reorganized how redirection is being done, and i've implemented
    auto-ACK for the i8259A, to reduce IRQ handling costs. One goal was to
    avoid the masking of the interrupt line for the timer interrupt on
    i8259A - but i think i'm going to revert that, it's causing too many
    problems all around.

    Ingo
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