A Framework for Block Placement, Migration, and Fast Searching in Tiled-DNUCA Architecture

Abstract

Multicore processors have proliferated several domains ranging from small-scale embedded systems to large data centers, making tiled CMPs (TCMPs) the essential next-generation scalable architecture. NUCA architectures help in managing the capacity and access time for such larger cache designs. It divides the last-level cache (LLC) into multiple banks connected through an on-chip network. Static NUCA (SNUCA) has a fixed address mapping policy, whereas dynamic NUCA (DNUCA) allows blocks to relocate nearer to the processing cores at runtime. To allow this, DNUCA divides the banks into multiple banksets and a block can be placed in any bank within a particular bankset. The entire bankset may need to be searched to access a block. Optimal bankset searching mechanisms are essential for getting the benefits from DNUCA. This article proposes a DNUCA-based TCMP architecture called TLD-NUCA. It reduces the LLC access time of TCMP and also allows a heavily loaded bank to distribute its load among the underused banks. Instead of other DNUCA designs, TLD-NUCA considers larger banksets. Such relaxations result in more uniform load distribution than existing DNUCA-based TCMP (T-DNUCA). Considering larger banksets improves the utilization factor, but T-DNUCA cannot implement it because of its expensive searching mechanism. TLD-NUCA uses a centralized directory, called TLD, to search a block from all the banks. Also, the proposed block placement policy reduces the instances when the central TLD needs to be contacted. It does not require the expensive simultaneous search as needed by T-DNUCA. Better cache utilization and a reduction in LLC access time improve the miss rate as well as the average memory access time (AMAT). Improving the miss rate and AMAT results in improvements in cycles per instructions (CPI). Experimental analysis found that TLD-NUCA improves performance by 6.5% as compared to T-DNUCA. The improvement is 13% as compared to the SNUCA-based TCMP design.