Arjan van de Ven wrote:
> On 9/20/2012 12:40 PM, Igor Zhbanov wrote:
>> But is it correct to consider ARM core to be offline when it is just in WFI state?
> nope
>
> for all intents and purposes, the cpu is still there.
>
> in an idle state, the cpu logically is there, and ready to resume execution if needed...
> that's the definition of idle ;-)
>
> offline is where the administrator takes a cpu out of circulation.
>
> neither specifies any physical hardware state... in fact offline is usually implemented as an idle state, at
> least on x86. the semantics for how to get back are different (system autonomous versus administrator)
>
> now, quite possible some ARM platforms abuse this and don't implement something as "idle" but as "offline" instead.
> that sounds not very smart to me.

Yes, it seems that on some ARM platforms offline and idle are mixed.
On my test device it is even hard to bring the core online. If I write 1 to "online" file,
then I see other pseudo-files only for a less than a second, then the core
will be brought offline again. It seems that kernel powers up the core, then sees that there
no task for it, and powers it down again.

May be we should talk to ARM developers to do things more correctly. It seems that now impossible
to administratively enable/disable some cores. The CPU governor will always consider all available
cores to be possible to use (except of limit of nr_cpus boot parameter).

So I don't know what to do best.

-- 
Best regards,
Igor Zhbanov,
Expert Software Engineer,
phone: +7 (495) 797 25 00 ext 3806
e-mail: i.zhbanov(a)samsung.com

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