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    SubjectRe: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option
    --Andrea Arcangeli <andrea@novell.com> wrote (on Sunday, September 12, 2004 16:17:01 +0200):

    > On Fri, Sep 10, 2004 at 05:34:21PM +0200, Arjan van de Ven wrote:
    >> disabling is actually not a bad idea; hard irq handlers run for a very short
    >
    > you mean hard irq handlers "should run" for a very short time. There can
    > be slow hardware that needs a long time, and fast hardware that needs a
    > short time, and in turn it makes perfect sense to allow nesting to give
    > low latency to the "fast" onces, like it has always happened so far (not
    > only in linux AFIK). Disabling nesting completely sounds a very bad
    > idea to me, when "limiting nesting" can be achieved easily as confirmed
    > by Alan too.

    IIRC, what we did in PTX was have 16 SPL levels, each interrupt was assigned
    a prio, and higher prio interrupts could interrupt lower prio ones (but not
    the same prio or higher). There's some support for that in the APIC, I think,
    something like the high nybble is prio, and the low nybble is just an index.

    M.

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