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Subject[patch] auto-limiting IRQ load take #2, irq-rewrite-2.4.11-F4

the attached patch contains a cleaned up version of IRQ auto-mitigation.

- i've removed the max_rate limit and have streamlined the impact of the
load-estimator on do_IRQ() to this piece of code:

if (unlikely(in_interrupt()))
goto mitigate_irqload;

i dont think we can get much cheaper than this. (We could perhaps avoid
the total_contexts counter by saving a 'snapshot' of the existing
kstat.irqs array of counters in every timer tick and comparing the
snapshot to the current kstat.irqs values. That looked pretty unclean

- the per-cpu irq counting in -D9 was incorrect as it collapsed all irq
handlers into a single counter.

- i've removed the net-polling hacks - they are unrelated to this problem.

the patch is against 2.4.11-pre2. (the eepro100.c fixes from the -ac tree
are already included in -pre2, i only included them in this patch to make
patching & testing against 2.4.10 easier.).

(i'd like to stress the point again that the goal of this approach is
*not* to be nice. This is an airbag mechanizm, it can and will hurt
performance. But my box does not lock up anymore.)

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