Efficient Metadata Management for Irregular Data Prefetching

Temporal prefetchers have the potential to prefetch arbitrary memory access patterns, but they require large amounts of metadata that must typically be stored in DRAM. In 2013, the Irregular Stream Buffer (ISB), showed how this metadata could be cached on chip and managed implicitly by synchronizing its contents with that of the TLB. This paper reveals the inefficiency of that approach and presents a new metadata management scheme that uses a simple metadata prefetcher to feed the metadata cache. The result is the Managed ISB (MISB), a temporal prefetcher that significantly advances the state-of-the-art in terms of both traffic overhead and IPC. Using a highly accurate proprietary simulator for single-core workloads, and using the ChampSim simulator for multi-core workloads, we evaluate MISB on programs from the SPEC CPU 2006 and CloudSuite benchmarks suites. Our results show that for single-core workloads, MISB improves performance by 22.7%, compared to 10.6% for an idealized STMS and 4.5% for a realistic ISB. MISB also significantly reduces off-chip traffic; for SPEC, MISB's traffic overhead of 70% is roughly one fifth of STMS's (342%) and one sixth of ISB's (411%). On 4-core multi-programmed workloads, MISB improves performance by 19.9%, compared to 7.5% for idealized STMS. For CloudSuite, MISB improves performance by 7.2% (vs. 4.0% for idealized STMS), while achieving a traffic reduction of 11x (96.2% for MISB vs. 1082.7% for STMS).