Re: userspace irq balancer

William Lee Irwin III
2003-05-27T01:57:10Z

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