[ale] Suggestions for 64 bit dual Opteron motherboards

[Dow Hurst]

Your right on with the 800MHz bus for the Xeons.  That is the weak link.  SGI 
has the Cray link technology which is a switched bus connected by routers all 
tuned to operate at the bandwidth required for memory, disk, and CPU 
interprocess communication to run at about 650Mbps.  (Someone correct me if 
I'm wrong)  That was the Origin 2K/3K architecture designed to never 
bottleneck at some point and grow in a seamless fashion.  I don't know how the 
Altix'es are designed but that has always been SGI's usual approach.  Design 
the top of the line so you can grow it forever and build it out the way you need.

Hypertransport is a similar idea, a switched network of 1.5Gb/s between CPUs. 
  Each CPU has it's own 1.5Gbps pipe to any other CPU.  Only currently scales 
to 8P as far as I know.  So 4 Xeons share in a hub like fashion the one 800MHz 
pipe to each other.
Dow


Jeffrey B. Layton wrote:
> Bjorn Dittmer-Roche wrote:
> 
>> On Fri, 23 Apr 2004, Dow Hurst wrote:
>>
>>  
>>
>>> I've been looking at performance of Opterons vs Itaniums/Xeons.  The 
>>> more
>>> Opterons on the motherboard the better.  So, 4P and 8P boards are out 
>>> there
>>> now.  Microway or Aspen have 4P units.  A Russian company has created 
>>> the 8P
>>> unit.  The Intel stuff is limited on interprocessor communication by 
>>> a single
>>> pipe while the Opterons have a switch like interconnect with much higher
>>> bandwidth.  The Xeon's top out and get starved by the limited pipe 
>>> they have
>>> to talk thru.  It is a long term problem Intel has gotten around for 
>>> now by
>>> bumping up CPU GHz.
>>>
>>> So you get a real increase in performance on the right kind of code 
>>> on a 4P+
>>> motherboard. ;-)
>>>
>>> I know your not after that info.  I just wanted to blab about what 
>>> I've been
>>> researching....
>>>   
>>
>>
>> I'm interested! I know this has been a long standing problem for intel.
>> One of the big advantages for years of companies like Sun
>> and SGI has been their ability to scale processors. Do
>> you happen to know how well the Opterons compare to these vendors?
>>
> 
> Scale in what way? Opterons have a neat memory bus (Hypertransport).
> I've only heard of systems going to 8-way, but I've heard rumors of
> 16-way systems though. The SGIs have a slightly different architecture.
> The processors are in a "network" configuration, like a Fat-Tree or
> a ring (couldn't think of a better work than "network", but that's not
> the right term) instead of having all of the processors on a single MB.
> Not sure how they compare, but I personally view them as separate
> products (although I'd love to see a 16-way Opteron, but I don't think
> AMD has a 1642 ot 1644 - at least not yet).
> 
> I tested one of our CFD codes on Opteron (242's I think) and compared
> them to Xeons/2.4 (800 MHz bus I think). On our code, the Opterons
> were faster by about 90% compared to the Xeons. YMMV.
> 
> Enjoy!
> 
> Jeff
> 
> 
> 
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> 

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Dow Hurst                  Office: 770-499-3428            *
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