Locality-Optimized Resource Alignment for Superdome 2

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Figure 1. Conceptual diagram of a Superdome 2 server
Interleaved memory
Interleaved memory (ILM) is a technique for masking the NUMA properties of a system. Successive
cache lines in the memory address space are drawn from different localities, making the average
memory access latency time more-or-less uniform. Whether memory is accessed sequentially or
randomly, every locality in the system will be used with equal probability.
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. For Superdome 2, local memory is referred to as Socket
Local Memory (SLM).