Re: Optimisation for smp_num_cpus loop in hotplug

[Pete Zaitcev <zaitcev@redhat.com>]

> 	for (i = 0; i < NR_CPUS; i++) {
> 		if (!cpu_online(i))
> 			continue;
> 
> Since the cpu online map is probably going to be quite sparse,
> could I suggest this alternative, which doesn't have to loop 32 times:

> +#define for_each_cpu(cpu, mask) \
> +       for(mask = cpu_online_map; \
> +           cpu = __ffs(mask), mask != 0; \
> +           mask &= ~(1<<cpu))
> +

This is neat, but I'd like to see it work with O(1) as well.
Mingo's code uses some long bitmaps.

-- Pete