Power saving in Multi core.

[Mulyadi Santosa]

Hi...

On Mon, Jun 13, 2011 at 15:26, naveen yadav <yad.naveen at gmail.com> wrote:
> Dear All,
>
> We are using ARM cortex a9. In below scenario, I want help.

May I take x86 as point of view here?

> Multi-Core Power Saving
> Hot plug feature allows for making a processor offline and let the
> system run as if there is only a single core.
> Now,comes the scenario - Let there are '2' cores in the system both
> running at a load of 40% (i.e. total load 80%), now in this case
> ideally '1' CPU is sufficient.
> So, if we make 2nd Core offline that will make the system execute
> everything on core '1'.

The thing is, you need to measure the real frequency step or, to be
precide, C/P state. If that 80 % on single processor, let's say
brought processor into highest C and P state *all the time*, there is
a chance the power consumption exceed 2 processor that by average in
mid or low C/P state (and they got chance to get idle more often too).

So physically, I agree 1 processor consume less power than 2
processor. But that depends entirely on the load. And, I believe it
also depends on which power scaling governor you use too.

> But will there be any power saving if we make any core offline under
> scenarios like this? Or will this have extra overhead?
> What are the pros and cons of working like this on Multi-Core?
>
> Regards
> Naveen
>
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-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
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