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    SubjectRe: userspace irq balancer
    William Lee Irwin III <wli@holomorphy.com> wrote:
    >> In
    >> the userspace implementation the reprogramming is done infrequently
    >> enough to make even significant cost negligible; in-kernel the cost
    >> is entirely uncontrolled and the rate of reprogramming unlimited.

    On Mon, May 26, 2003 at 06:59:20PM -0700, Andrew Morton wrote:
    > eh?
    > #define MAX_BALANCED_IRQ_INTERVAL (5*HZ)
    > #define MIN_BALANCED_IRQ_INTERVAL (HZ/2)

    The number of interrupt sources on a system ends up scaling this up to
    numerous IO-APIC RTE reprograms and ioapic_lock acquisitions per-second
    (granted, with a 5s timeout between reprogramming storms) where it
    competes against IO-APIC interrupt acknowledgements.

    Making the lock per- IO-APIC would at least put a bound on the number
    of competitors mutually interfering with each other, but a tighter
    bound on the amount of work than NR_IRQS would be more useful than that.


    -- wli
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