[MakeLV] Question on power usage of multicore CPUs

[Randy Kramer]

Thanks!  Interesting article, the kind I'll have to read at least a second 
time to make more sense of it. 

At a first cut, it looks like Intel might do better at turning off cores to 
save power.  But, iiuc, they both increase the speed on the utilized cores 
when other cores are unused, thus boosting the power used.  
   
AMD seems to do that in groups of 3 (on a 6 CPU chip), Intel seems able to do 
it per CPU.  

It's not yet clear to me whether, well let's consider the AMD, and a load that 
is single threaded:  will that single threaded application cause 3 of the 
CPUs to run at the boosted speed and thus the chip continue to use almost the 
full rated power (for example, 125 watts if the multicore chip is rated at 
125 watts).

I suspect it might.

Randy Kramer

On Tuesday 03 April 2012 12:38:53 pm Keith Erekson wrote:
> Modern multi-core CPUs have the ability to disable unused cores (as
> long as the OS supports it?), and also to overclock a core (or two?)
> if it's the only one being used.
>
> A quick google turned up this article, from about 2 years ago, that
> seems like it has a good overview of the different tech behind Intel's
> and AMD's versions of this concept:
>
> http://www.pcper.com/reviews/Processors/AMDs-Turbo-Core-Technology
>
> ~Keith
>
> On 04/03/2012 12:30 PM, Randy Kramer wrote:
> > I don't see much traffic on the old LVLUG lists, so I thought I'd
> > try asking my question here, first.
> >
> > A few months ago, I got a really good deal on a motherboard for an
> > AMD AM-3 socket CPU. ($15 after rebate.)
> >
> > I had intentions of watching for a low power CPU with maybe 2 cores
> > come on sale. So far, almost everything I've seen on sale is rated
> > for 95 watts, which is more than I'd like to use. (Btw, 95 watts
> > is the maximum rating for the board.)
> >
> > So, I got to thinking--I don't think most software takes full
> > advantage of multicore CPUs, so I'm guessing that even if I bought
> > something with 4 or more cores, most of the time I'd be using only
> > 1 or 2.
> >
> > Thus, if I bought a 4 core CPU rated at 95 watts, most of the time
> > I'd be using significantly less than 95 watts.
> >
> > I realize there would be some logic that would be energized on
> > those cores even if not used, as well as more "infrastructure"
> > logic than if I had a one or two core CPU, but I'd still expect
> > substantially less power usage.
> >
> > Am I way off base?
> >
> > Randy Kramer
> >
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