Very good remark Jim,
Another complicating factor is that for intel and amd there is
definitely ready available libraries written in assembly that are
lightning fast,
whereas for C* type processors i can't remember there is much, as
your "more Ghz into battle is better rule" always means that the C*
chip is gonna be slower anyway,
also in future incarnations over intel&amd, so why bother writing
good libraries for that chip?
Vincent
On Nov 8, 2007, at 11:43 PM, Jim Lux wrote:
At 11:04 AM 11/8/2007, Peter St. John wrote:
Vincent,
That's tough for me to answer, presumably the 1.5 is cheaper per
hertz
in power than a 3 GHz, but because of the other issues it may not be
cheaper in GFLOPS per power. No hablo EE.
Peter
On Nov 8, 2007 1:58 PM, Vincent Diepeveen <[EMAIL PROTECTED]> wrote:
> For a compute cluster wouldn't it be a thought to also consider the
> cost of 3 years of nonstop electricity for the amount of gflops it
> delivers?
>
In general, a N GHz processor will be poorer in a flops/Watt sense
than a 2N GHz processor.
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.
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.
Complicating this all is:
a) A significant fraction of the load in a PC is all the other
stuff that's toggling back and forth, like memory address and data
lines. This will be driven more by the FSB speed, which might be
the same for the two processors.
b) You may have a lower core voltage, but the regulator making that
voltage may or may not be as efficient.
c) Power supply efficiency can vary a LOT from model to model. All
the way from 50% for a really crummy design to 95% for a good design.
d) Faster processors aren't necessarily architecturally identical
to slower processors. They may have different pipeline depths,
different microcode, different ALU strategies, etc. It's not just
a matter of shrinking the masks and turning up the clock.
Jim
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