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 _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
