> >> Btw is it correct that one could also use the APIC Task Priority Registers
> >> to implement "fair" IRQ routing? (If linux adjusted them, which it
> >> currently doesn't).
> >
> > Yes, and Dave Olien has already done this. It's a good idea for P3,
> > and seems to me to be essential for P4.
another problem with TPR-based IRQ routing (in addition to the ones i
mentioned in the previous mail) is that if you 'deny' certain IRQs via the
TPR, then if all CPUs run kernel-intensive jobs, then IRQs will never be
served by any of the CPUs (or will be served only after a long latency).
Sure, this can be hacked around, but if gets ugly very fast and doesnt get
us very far. All in one, i found the TPR to be not flexible enough for
what we really want: good IRQ distribution and good IRQ affinity at once.
Ingo
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