Optimizing Home-Based Software DSM Protocols

Software DSMs can be categorized into homeless and home-based systems both have strengths and weaknesses when compared to each other. This paper introduces optimization methods to exploit advantages and offset disadvantages of the home-based protocol in the home-based software DSM JIAJIA. The first optimization reduces the overhead of writes to home pages through a lazy home page write detection scheme. The normal write detection scheme write-protects shared pages at the beginning of a synchronization interval, while the lazy home page write detection delays home page write-protecting until the page is first fetched in the interval so that home pages that are not cached by remote processors do not need to be write-protected. The second optimization avoids fetching the whole page on a page fault through dividing a page into blocks and fetching only those blocks that are dirty with respect to the faulting processor. A write vector table is maintained for each shared page in its home to record for each processor which block(s) has been modified since the processor fetched the page last time. The third optimization adaptively migrates home of a page to the processor most frequently writes to the page to reduce twin and diff overhead. Migration information is piggybacked on barrier messages and no additional communication is required for the migration. Performance evaluation with some well-accepted benchmarks and real applications shows that the above optimization methods can reduce page faults, message amounts, and diffs dramatically and consequently improve performance significantly.