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SubjectRe: [PATCH] Resurect proper handling of maxcpus= kernel option


Ingo Molnar wrote:
> * Max Krasnyansky <maxk@qualcomm.com> wrote:
>
>>> This will need some test time on 32-bit as that is where this
>>> represents a material change. ( albeit what matters most is the
>>> maxcpus=1 distinction - and for that nosmp can be used as well to
>>> turn off multi-cpu support altogether. So we could do this in
>>> v2.6.27 as well. )
>> So far we got a couple of reports that it works as expected on 32
>> (both laptop and server/desktop).
>
> Yes, but the usecase i'm worried about is when say maxcpus=1 was used to
> _prevent_ an SMP bootup - because the system would not work otherwise.
>
> i guess we want to tickle those systems anyway as that case is not
> supposed to happen (and it can always be totally disabled via nosmp or
> noapic).
>
> So i'm not against your fix/change per se, i just wanted to highlight
> that it has some impact on existing uses of maxcpus that is outside of
> your cpu-hotplug usecase.

I see what you mean. I think it's fairly safe though since we do not actually
do much for the cpus that are not going to be brought online. Mainly just
setting cpu_*_map and initializing per cpu areas. If something is broken in
there we'd probably want to fix that asap anyway. And like you said nosmp does
the job too.

Max


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