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    SubjectRe: [PATCH] warn about shared irqs requesting IRQF_DISABLED registered with setup_irq
    Russell King - ARM Linux wrote:
    > On Sun, Nov 29, 2009 at 03:18:40PM +0000, Jamie Lokier wrote:
    > > Or we could do away with this silliness and just switch everything to
    > > threaded interrupts with RT-priorities ;-)
    > ... thereby needlessly increasing the latency of all interrupt handling
    > and probably breaking some devices.

    It's not that cut and dried. RT gives you priorities where you might
    not have had them before, so in some cases can reduce worst-case
    latency for critical devices. IRQF_DISABLED is a cheap two-level
    priority scheme; RT threaded interrupts extend it.

    The extra processing increases latency, yes, but that is in a sense a
    scheduling fast-path problem; it's not _intrinsic_ to threaded
    interrupts that they have to have higher latency (you don't have to
    use the normal calculation or task switch to get equivalent
    behaviour), but undoubtedly trying to optimise that leads to very
    twisty code and state representations, and I don't see it happening in
    Linux any time soon.

    -- Jamie

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