Influence of Architectural Features of the SNC-4 Mode of the Intel Xeon Phi KNL on Matrix Multiplication
The Sub-NUMA Clustering 4 (SNC-4) affinity mode of the Intel Xeon Phi Knights Landing introduces a new environment for parallel applications, that provides a NUMA system in a single chip. The main target of this work is to characterize the behaviour of this system, focusing in nested parallelization for a well known algorithm, with regular and predictable memory access patterns as the matrix multiplication. It has been studied the effects of thread distribution in the processor on the performance when using SNC-4 affinity mode, the differences between cache and flat modes of the MCDRAM and the improvements due to vectorization in different scenarios in terms of data locality. Results show that the best thread location is the scatter distribution, using 64 or 128 threads. Differences between cache and flat modes of the MCDRAM are, generally, not significant. The use of optimization techniques as padding to improve locality has a great impact on execution times. Vectorization resulted to be efficient only when the data locality is good, specially when the MCDRAM is used as a cache.
keywords: Intel Xeon Phi KNL, SNC-4, MCDRAM, Vectorization