LMStr: Local memory store the case for hardware controlled scratchpad memory for general purpose processors

In this paper, we present a hardware controlled on-chip memory called Local Memory Store (LMStr) that can be used either solely as a scratchpad or as a combination of scratchpad and cache, storing any variable specified by the programmer or extracted by the compiler. LMStr is different than a traditional scratchpad in that it is hardware-controlled and it stores the same type of variables in a block that is allocated based on availability and demand. In this initial work on LMStr, we focus on identifying the potential for LMStr, namely, the advantages of storing temporary and program variables in blocks in LMStr and comparing the performance against a regular cache. To the best of our knowledge, this is the first work where scratchpad has been used in a generalized way where the focus is on storing temporary and programmer specified variables in blocks. We evaluate LMStr on a micro-benchmark and a set of the mini-applications in the mantevo suite. We simulate LMStr in the Structural Simulation Toolkit (SST) simulator. LMStr provides a 10% reduction in average data movement between on-chip and off-chip memory compared to a traditional cache hierarchy.