A Best-Offset Prefetcher

The Best-Offset (BO) prefetcher submitted to the DPC2 contest prefetches one line into the level-two (L2) cache on every cache miss or hit on a prefetched line. The prefetch line address is generated by adding an offset to the demand access address. The BO prefetcher tries to find automatically an offset value that yields timely prefetches with the highest possible coverage and accuracy. It evaluates an offset value by maintaining a table of recent requests addresses and by searching these addresses to determine whether the line currently requested would have been prefetched in time with that offset. The paper is organized as follows. Section 1 presents offset prefetching. Section 2 describes the proposed BO prefetcher. Section 3 describes a prefetch throttling mechanism (somewhat specific to DPC2) for dealing with situations where prefetch hurts performance. Section 4 mentions related prefetchers. Finally, Section 5 presents a few simulation results.