[Beowulf] The Walmart Compute Node?

Peter St. John peter.st.john at gmail.com
Fri Nov 9 11:58:55 EST 2007


Vincent,
I'm missing something in the arithmetic. "3 nodes of quadcore" is 12
cores? delivering 100 "GFlops" would require something like 8 GHz? So
perhaps you mean, 3 nodes of dual socket, quadcore CPU  (24 cores) at
4GHz? And you can get that for $1500?
Thanks,
Peter

On Nov 9, 2007 11:44 AM, Vincent Diepeveen <diep at xs4all.nl> wrote:
> 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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