[Beowulf] The Walmart Compute Node?

Vincent Diepeveen diep at xs4all.nl
Fri Nov 9 11:44:26 EST 2007


Larry, all what you write is very interesting and of course i hope  
for you your product line gets a big succes.
Just like IBM's blue gene, the major expertise of your product line  
is that it is only interesting to governments who need major amounts of
crunching power (the other conditions left aside such as no big RAM  
requirements as that usually means you need good branch prediction  
and so on),
and who have million dollar budgets, and probably have a program  
lying around where this hardware can get used for.

The price of a box with say 100 "1 gflop" cpu's, delivering in total  
100 gflop isn't gonna be $1500 i guess, whereas for 1500$ one can  
build hands down
3 nodes with a quadcore, delivering not only *more* than 100 gflop,  
but also capable of doing other software than just crunching; it's  
also possible to put
a lot of RAM inside and it's also possible to run software that's  
making a lot of use from the branch predictor.

For sure you're not qualifying for a $2500 setup, and with those  
freak qualifications you qualify bigtime for this mailing list of  
course :)

On Nov 9, 2007, at 3:42 PM, Larry Stewart wrote:

> Robert G. Brown wrote:
>
>> On Thu, 8 Nov 2007, Jim Lux wrote:
>>
>>> In general, a N GHz processor will be poorer in a flops/Watt  
>>> sense than a 2N GHz processor.
>>
> Well that just isn't so.  It seems pretty clear from IBMs BlueGene/ 
> L, as well as the SiCortex processors, that the
> opposite is true.  The new Green 500 list is brand new, and there's  
> not much on it yet, but the BG/L is delivering 190MF/Watt
> on HPL, whereas the machines made out of Intel and AMD chips are  
> half that at best.
>
>>>
>>> The power draw is a combination of a fixed load plus a frequency  
>>> dependent load, so for the SAME processor, running it at N/2 GHz  
>>> consumes more than 50% of the power of running it at N GHz.
>>
> This probably IS true, but high performance cores have a lot more  
> logic in them to try to achieve performance: out of order
> execution, complex branch prediction, register renaming, etc. etc.   
> A slower core can be a lot simpler with the same silicon process,
> so a decent lower-clock design will be more power efficient than a  
> fast clock design.
>
>>>
>>> If you go to a faster processor design, the frequency dependent  
>>> load gets smaller (smaller feature sizes= smaller capacitance to  
>>> charge and discharge on each transition).  The core voltage is  
>>> also usually smaller on higher speed processors, which also  
>>> reduces the power dissipation (smaller number of joules to change  
>>> the voltage from zero to one or vice versa).  So, in general, a  
>>> 2N GHz processor consumes less than twice the power of a N GHz  
>>> processor.
>>
> The flaw in this argument is that a slower clock design can use the  
> same small transistors and the same current state of the art  
> processes and it will use many fewer transistors to get its work  
> done, thus using very much less power.  Our 1 GF core is 600  
> milliwatts, for example.
> Even after adding all the non-core stuff - caches, memory  
> controllers, interconnect, main memory, and all overhead, it is  
> still around 3 watts per GF.
>
>>
>> In ADDITION to this is the fact that the processor has to live in a
>> house of some sort, and the house itself adds per processor overhead.
>> This overhead is significant -- typically a minimum of 10-20 W,
>> sometimes as much as 30-40 (depending on how many disks you have, how
>
> This factor does not scale this way!  With low power processors,  
> you can pack them together, without the endless support chips, you
> can use low power inter-chip signalling, you can use high  
> efficiency power supplies with their economies of scale.  If you  
> look inside
> a PC there are two blocks doing useful work - memory and CPUs, and  
> a whole board full of useless crap.  Look inside a machine designed
> to be a cluster and there should be nothing there but cpus and memory.
>
>
> -- 
> -Larry / Sector IX
>
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