[Beowulf] memory bandwidth scaling

[Orion Poplawski]

On 10/02/2015 02:30 AM, John Hearns wrote:
> Orion, that is a good question.
>
> I have to say though that we are heading for a world where you don't get to make that choice - the lowest core count SKUs will just get higher and higher.
> Couple this with the current way many folks specify systems with a minimum amount of RAM per core (which is quite sensibly based on looking at their applications and how much memory they consume!) also is leading us to specify higher memory for two processor nodes,
> and to keep a balanced DIMM configuration too. I was discussing this with some researchers only yesterday.
>
> I will throw something open to the floor:
> You don't HAVE to use all the cores in a CPU socket.
> Yes, I realise that you have paid for them and that they are a resource which is available.

Well, that's the rub.  If we compare:

DUAL INTEL XEON 6C E5-2620V3 (2.4GHz/8GT/s/15MB)            $870
DUAL INTEL XEON 12C E5-2670V3 (2.3GHz/9.6GT/s/30MB) CPU  [+$2400.00]

So for the marginal cost we're close to being able to buy a whole other 
node.  I haven't paid for anything yet so I'm trying to feel out if it's 
worth going for the higher core counts.  As usual "it depends", but just 
curious what people's experience has been.

>
> I am perhaps not explaining myself very well, and I imagine lots of sites already allocate different numbers of cores per node depending on job type.
>
>
>
>
> We may be looking a getting a couple new compute nodes.  I'm leery though of going too high in processor core counts.  Does anyone have any general experiences with performance scaling up to 12 cores per processor with general models like CM1/WRF/RAMS on the current crop of Xeon processors?
>
> --
> Orion Poplawski
> Technical Manager                     303-415-9701 x222
> NWRA, Boulder/CoRA Office             FAX: 303-415-9702
> 3380 Mitchell Lane                       orion at nwra.com
> Boulder, CO 80301                   http://www.nwra.com
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-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  orion at cora.nwra.com
Boulder, CO 80301              http://www.cora.nwra.com