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SubjectRe: [announce] [patch] limiting IRQ load, irq-rewrite-2.4.11-B5
Sorry, if I missed something in the patch, but here is a question.

Shouldn't the interrupt mitigation be on a per CPU basis?
What I mean is that if a particular CPU is hogged due to some
interrupt, that interrupt should be mitigated on that particular CPU
and not on all CPUs in the system. So, unless an interrupt ends up
taking a lot of time on all CPUs it should still have a chance to
do something.

This could probably help in distributing the interrupts more evenly and
fairly on an SMP system or vice-versa.


Ingo Molnar wrote:

>On Thu, 4 Oct 2001, BALBIR SINGH wrote:
>>Ingo, is it possible to provide an interface (optional interface) to
>>drivers, so that they can decide how many interrupts are too much.
>well, it existed, and i can add it back - i dont have any strong feelings
>>Drivers who feel that they should go in for interrupt mitigation have
>>the option of deciding to go for it.
>in those cases the 'irq overload' code should not trigger. It's not the
>rate of interrupts that matters, it's the amount of time we spend in irq
>contexts. The code counts the number of times we 'interrupt and interrupt
>context'. Interrupting an irq-context is a sign of irq overload. The code
>goes into 'overload mode' (and disables that particular interrupt source
>for the rest of the current timer tick) only if more than 97% of all
>interrupts from that source 'interrupt and irq context'. (ie. irq load is
>really high.) As any statistical method it has some inaccuracy, but
>'statistically' it gets things right.
> Ingo

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