Re: [patch 1/1] export cpu_online_map

[Andrew Morton]

Paul Jackson <pj@xxxxxxx> wrote:
>
> Andrew wrote:
> > Sweet, thanks.  Perhaps we can remove cpu_online_map from UP builds soon -
> > it's really wrong to have it there.
> 
> Eh ... my gut reaction is different.   Even uni-processors have
> online cpus - just not very many of them (and hot unplugging one
> of them is frowned on).

That's daft.  A uniprocessor machine has one and only one CPU and it's
always online!   An online_map is only needed for MP.

Now conceptually, yes, we should be able to query and perhaps set the
onlineness of a CPU.  But that doesn't mean that we should have storage
which idiotically remembers something which was known at compile time.

>  Why make special cases when it serves no purpose?

Ths presence of cpu_online_map in UP builds _is_ a special case.  The
kernel's overall approach to such things is to optimise them away at
compile time for !SMP builds.

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