[Beowulf] slightly [OT] smp boxes

Prentice Bisbal prentice at ias.edu
Fri Oct 17 10:28:46 PDT 2008

andrew holway wrote:
> Hi
> If you wanted to buy an smp machine of 8, 16 or 32 sockets, what would
> be your options?

Do you really mean SMP, or just 8, 16, or 32 nodes in the same box,
running a single system image (SSI) of the OS?

Having a system with 8, 16, or 32 sockets does not necessarily equal
SMP. Any Opteron based multiprocessor system is actually a NUMA system,
since each Opteron has it's own memory controller on-chip and own bank
of DIMMs.

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?)

If you just want an SSI, and NUMA is acceptable, you can look at the SGI
Altix systems. They use SGI's NUMAlink (TM) Architecture to scale up the
# of processors while behaving as a single NUMA system. The first Altix
systems used Itanium processors which aren't binary compatible with x86
processors (a real inconvenience) if you were planning on running
commercial, binary-only x86 software) but there are newer Altix systems
(XE series) that use x86-based processors.


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.


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