2002 | OriginalPaper | Buchkapitel
Minerva: An Adaptive Subblock Coherence Protocol for Improved SMP Performance
verfasst von : Jeffrey B. Rothman, Alan Jay Smith
Erschienen in: High Performance Computing
Verlag: Springer Berlin Heidelberg
Enthalten in: Professional Book Archive
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We present a new cache protocol, Minerva, which allows the effective cache block size to vary dynamically. Minerva works using sector caches (also known as block/subblock caches). Cache consistency attributes (from the MESI set of states) are associated with each 4-byte word in the cache. Each block can itself have one of the attributes invalid, exclusive or shared. Each block also has a current subblock size, of 2k words and a confidence value for hysteresis. The subblock size is reevaluated every time there is an external access (read or invalidate) to the block. When a fetch miss occurs within a block, a subblock equal to the current subblock size is fetched. Note that the fetch may involve a gather operation, with various words coming from different sources; some of the words may already be present.Depending on the assumed cache sizes, block sizes, bus width, and bus timings, we find that Minerva reduces execution times by 19-40%, averaged over 12 test parallel programs. For a 64-bit wide bus, we find a consistent execution time reduction of around 30%. Our evaluation considers the utility of various other optimizations and considers the extra state bits required.