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SubjectRe: Optimisation for smp_num_cpus loop in hotplug
From said:
> Yeah, it's simple, and none of the current ones are really critical.
> But I think we're better off with:
> for (i = first_cpu(); i < NR_CPUS; i = next_cpu(i)) {

> Which is simple enough not to need an iterator macro, and also has the
> bonus of giving irq-balancing et al. an efficient, portable way of
> looking for the "next" cpu.

So you're thinking that next_cpu(i) is something like

__ffs((~(unsigned)((1<<i)-1) & cpu_online_map)

plus an extra exception piece to take next_cpu(i) above NR_CPUS if we have no
remaining CPUs (because __ffs would be undefined)? It's the exception piece
that I don't see how to do really efficiently.


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