A Low-Complexity Synchronization Based Cache Coherence Solution for Many Cores

Computer architectures make a dramatic turn away from improving single-processor performance towards improved parallel performance through integrating many cores in one chip. However, providing directory based coherence protocols for these platforms is too complex and expensive. As a substitute, we propose a synchronization based cache coherence solution, which uses different cache policies according to three flexible software guided scopes (exclusion, producer and consumer scopes) to solve the data-race and coherence problem. Furthermore, this protocol implements word dirty bits (only one bit per word is needed in each L1 cache line) and a special hardware synchronization manager (HSM) to support multi-writer, the write-validate policy and to eliminate the remote un-cache spinning at the ldquoflagrdquo. We evaluate Godson-T, a platform supporting this protocol, against an idealized interleaved dual tag directory based protocol on the Splash2 and two bioinformatics benchmarks. The performance of the synch-based protocol is degraded only at 3.2% on average, but the real chip area is reduced at 32% even if the overhead of HSM is included.