[Beowulf] XEON power variations

[Joe Landman]

Tom Rockwell wrote:
> Hi,
> 
> Intel assigns the same power consumption to different clockspeeds of L, 
> E, X series XEON.  All L series have the same rating, all E series etc.  

Not quite.  They provide the maximum power consumption/dissipation, and 
quite possibly bin these numbers over a range of parts.

> So, taking their numbers, the fastest of each type will always have the 
> best performance per watt.  And there is no power consumption penalty 

Well ... against the TDP bin, not necessarily in actuality.

> for buying the fastest clockspeed of each type.  Vendor's power 
> calculators reflect this (dell.com/calc for example).  To me this seems 

These numbers come from Intel in most cases.

> like marketing simplification...  Anybody know any different, e.g. have 

binning.

> you seen other numbers from vendors or tested systems yourself?

We have a 2.93GHz Nehalem and a 3.2 GHz Nehalem that are almost 
identical.  We could put a power meter on them if you'd like (I bought 
one a while ago for this purpose).

I've found from a design perspective, that its always a better idea not 
to design for actual power, but to design for maximim power consumed, 
and then add some margin.

Its far better to overestimate your power and cooling needs than to 
underestimate it.

> Is the power consumption of a system with an E5502 CPU really the same 
> as one with an E5540?

It's worth noting that the E5502 CPU is a 1.86GHz part, while E5540 is a 
2.53GHz part.  The power consumed in a CPU is a function of frequency. 
A linear dependence upon frequency would have the E5540 being 36% more 
power than the E5502.  However, the 5502 is a dual core part, and the 
5540 is a quad core part, so you get 2x the number of FLOPs out of the 
5540.  This would bias the performance per watt calculation if it 
weren't factored in correctly.



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Joseph Landman, Ph.D
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