[Beowulf] slightly [OT] smp boxes

Tom Elken tom.elken at qlogic.com
Fri Oct 17 12:21:07 PDT 2008

> [mailto:beowulf-bounces at beowulf.org] On Behalf Of Prentice Bisbal
> If you just want an SSI, and NUMA is acceptable, you can look at the
> Altix systems. They use SGI's NUMAlink (TM) Architecture to scale up
> # of processors while behaving as a single NUMA system. The first
> systems used Itanium processors which aren't binary compatible with
> processors (a real inconvenience if you were planning on running
> commercial, binary-only x86 software) but there are newer Altix
> (XE series) that use x86-based processors.
> http://www.sgi.com/products/servers/altix/xe/

But the Altix XE and Altix ICE systems with x86_64 processors are
essentially clusters with 2 sockets per node -- so not meeting the >=
8-socket SMP box desires of the original poster.

> <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.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.


> If you want that many processors in a single system, you probably do
> want NUMA, since the single memory controller for that many processors
> will become a bottleneck.
> -- 
> Prentice
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