The performance impact of false subpage sharing in KSR1

This paper presents insight into important aspects of the performance of KSR1 multiprocessor. We report performance degradations caused by false sharing of memory subpages (128 bytes long units of transfer and consistency) between local caches in the KSR1. In other words, the performance is measured when multiple processing nodes issue simultaneous write requests for a single subpage. Our measurements show that low level knowledge about the organization of the ALLCACHE memory and explicit use of non-shared variables in parallel threads can result in performance improvement of almost an order of magnitude. However, writing such programs is much closer to distributed memory MIMD programming than shared memory programming.<
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