Locality-Optimized Resource Alignment

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Sometimes interleaved memory is the best technique. ILM yields good performance when memory
references are spread across the entire address space with equal probability. This is the case for
applications using large global data sets with no spatial locality.
Local memory
If memory is not interleaved, then the natural localities inherent in the structure of the server complex
are evident. The processor cores in each locality enjoy fast access to their local memory. The
counterpoint is that access to memory in a different locality is slower. When the memory reference
pattern places the majority of accesses in local memory, LORA gives a significant performance
advantage relative to interleaved memory.
LORA scope
Hardware platforms
LORA applies only to those HP servers that have a Non-Uniform Memory Architecture. Those are the
servers built around the sx1000 and sx2000 chip sets.
For these servers, the localities are oriented around cells. Local memory is referred to as Cell Local
Memory (CLM).
Memory performance is better when all the cells in an nPartition have the same amount of memory
installed. This is good advice for the 100% interleaved case, because the deepest interleave is
possible only when each cell contributes the same amount of memory. Having the same amount of
memory on each cell is even more important for LORA: the memory symmetry promotes balanced
utilization of the processing resources. Asymmetry of local memory can cause a slight degradation in
overall system performance.
The Integrity platform is the design center for LORA, and the architecture exploits features specific to
that platform. LORA is not supported on HP 9000 (PA-RISC) platforms.
Operating system
Update 3 to HP-UX 11i v3, released in September 2008, was the first version to provide a rich set of
mechanisms to support local memory. We recommend that LORA be used with this update or its
successors, Update 4 and Update 5.
The earliest versions of HP-UX assumed a uniform memory architecture and implemented only the SMP
mode. HP-UX 11i v2 was the first version to provide support for local memory. The entire burden for
managing local memory is placed on the system administrator and on applications, so we do not
recommend LORA with HP-UX 11i v2.
Virtual partitioning
The two virtual partitioning solutions provided by HP are Virtual Partitions (vPars) and Integrity Virtual
Machines. Because these solutions subdivide the physical resources of an nPartition, they present
opportunities to exploit locality.
The virtualization model of vPars is particularly well-suited to LORA. The version of the T1335DC
product first delivered in Update 4 to HP-UX 11i v3, version A.05.05, contains many optimizations to
gain additional benefit from local memory.
The binding of virtual resources to physical resources in Integrity Virtual Machines is flexible and fluid,
yet there are still opportunities to gain performance advantage through resource alignment. HP
recommends deploying Integrity Virtual Machines with LORA starting with Update 4.