[Beowulf] AMD Roadrunner open compute motherboard

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Sat Jan 19 07:08:38 PST 2013



On 1/18/13 10:03 PM, "Greg Lindahl" <lindahl at pbm.com> wrote:

>On Fri, Jan 18, 2013 at 03:00:11PM -0500, Mark Hahn wrote:
>> > As in contradiction to what Mark Hahn says - it needs active cooling.
>> 
>> if anyone cares: a dimm dissipates roughly 2W, depending on generation,
>> whether it's LV, number of devices, etc.  one of those duplex 14krpm
>>fans 
>> is typically rated at about 12W.
>
>Every time I've tried to load systems up with RAM and measure an
>increase in power consumption, I haven't been able increase it.  And I
>tried a variety of intense memory access patterns. Maybe someone else
>has done this experiment and gotten different results?
>
>> so even a 1W device needs some airflow, but it's mostly CPUs that count.
>
>Yep.
>

I think the "few watts" for the DRAM is insignificant next to the CPU
loading..

You raise an interesting point, though, on what the load dependency of the
DRAM dissipation might be, and how one would change it.  For one thing,
you're always hitting the ram for refresh purposes.

What you *might* be able to do is put temperature probes on two banks of
memory, and then run a program that hits both banks, vs a program that
hits just one, and look for a difference.



>



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