Interrupt mitigation

Limit the max rate at which a card can generate interrupts.

Built-in in some cards (recent 21143, fxp with new microcode)

Can be emulated in software (have patches for intr_machdep.c), disable individual interrupt lines till next clock tick.

Pros and cons

no need for per-device modifications

partly reduces interrupt overhead

still potentially subject to livelock and responsivity problems;

when interrupts are shared, all devices on the same line are delayed;