[Beowulf] slightly [OT] smp boxes
prentice at ias.edu
Fri Oct 17 13:43:35 PDT 2008
Tom Elken wrote:
>> 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
>> 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?)
> 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.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.
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
**Hennessy, John L, and Patterson, David A., "Computer Architecture: A
Quantitative Approach", 3rd Ed., Morgan Kaufman Publishers, 2003
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