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SubjectRE: [PATCH] Fix hotplug cpu on x86_64
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> > sure convenient. I though at the time it would be great if
> > alloc_percpu() mechanism was able to dynamically re-create all the
> > per_cpu's for new processors, that way cpu_possible_map woun't
> > probably even be needed. Or is it too much trouble for too
> little gain...
>
> The problem is to tell all subsystems to reinitialize the
> data for possible CPUs (essentially the concept of "possible"
> CPUs would need to go) It would need an reaudit of a lot of
> code. Probably quite some work.

You know Andi, I was imagining something like bitmap or linked list of
all per_cpu vars (dynamically updated) and just going through this
list... Or something like that (maybe some registration mechanism).
There are not too many of them - about two dozens, mostly all sorts of
accounting.

> I think it is better to try to figure out how many hotplug
> CPUs are supported, otherwise use a small default.

Exactly - such as on ES7000, it can support 32, 64, 128 etc. processors
depending on what configuration the customer actually ordered :)... it
should be something for that, then NR_CPUS could be either defined as
boot parameter or belong to subarchs.
Thanks,
--Natalie

> My
> current code uses disabled CPUs as a heuristic, otherwise
> half of available CPUs and it can be overwritten by the user.
>
> -Andi
>
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