[Beowulf] slightly [OT] smp boxes

Prentice Bisbal prentice at ias.edu
Fri Oct 17 16:43:35 EDT 2008


Tom Elken wrote:
>> <aside>
>> To split hairs, in a system with multi-core Opterons, the cores on a
>> single chip are SMP relative to each other, since they all 
>> use the same
>> memory controller, and have equal access to the RAM directly 
>> controlled
>> by that memory controller. But once they access RAM from another chip
>> (different socket), it becomes a NUMA situation. (Is there a name for
>> this hybrid architecture?)
>> </aside>
> 
> NUMA != SMP is not a universally held conclusion.
> 
> By some definitions*, SGI's large Altix machines, NUMA with Itanium, are
> SMP machines.  Each processor core in these Altix's can read/write from
> any memory in the machine (with differing latency), and access the I/O
> resources of the machine.
> Press releases certainly trumpet them that way: "NCSA Adds 6.5 Teraflops
> With SGI Altix SMP System" at 
> http://www.hpcwire.com/offthewire/17869149.html
> 
> 
> * http://www.webopedia.com/TERM/S/SMP.html
> "Short for Symmetric Multiprocessing, a computer architecture that
> provides fast performance by making multiple CPUs available to complete
> individual processes simultaneously (multiprocessing). Unlike
> asymmetrical processing, any idle processor can be assigned any task,
> and additional CPUs can be added to improve performance and handle
> increased loads. A variety of specialized operating systems and hardware
> arrangements are available to support SMP. Specific applications can
> benefit from SMP if the code allows multithreading.
> 
> SMP uses a single operating system and shares common memory and disk
> input/output resources. Both UNIX and Windows NT support SMP. "
> 
> Altix with Itanium satisfies this definiton.

I always considered SMP to refer the memory access model, purely from a
hardware perspective, but as your post and several other replies have
indicated, there's differing opinions on this, and definitely no
universal consensus.  Interestingly, Wikipedia agrees with my earlier
statements*, which is in opposition to webopedia's def.

http://en.wikipedia.org/wiki/Symmetric_multiprocessing

I consulted Hennessy & Patterson** to see what they said, but, they are,
uhhhh... to verbose for a Friday afternoon.

* I didn't read the *whole* entry, but skimmed it quickly while writing
this.

**Hennessy, John L, and Patterson, David A., "Computer Architecture: A
Quantitative Approach", 3rd Ed., Morgan Kaufman Publishers, 2003


-- 
Prentice
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