A software-controlled prefetching mechanism for software-managed TLBs

Abstract

The TLB (Translation Lookaside Buffer) miss services have been concealed from operating systems, but some new RISC architectures manage the TLB in software. Since software-managed TLBs provide flexibility to an operating system in page translation, they are considered an important factor in the design of microprocessors for open system environments. However, software-managed TLBs suffer from larger miss penalty than hardware-managed TLBs, since they require more extra context switching overhead than hardware-managed TLBs.

This paper introduces a new technique for reducing the miss penalty of software-managed TLBs by prefetching necessary TLB entries before being used. This technique is not inherently limited to specific applications. The key of this scheme is to perform the prefetch operations to update the TLB entries before first accesses so that TLB misses can be avoided. Using trace-driven simulation and a quantitative analysis, the proposed scheme is evaluated in terms of the miss rate and the total miss penalty. Our results show that the proposed scheme reduces the TLB miss rate by a factor of 6% to 77% due to TLB characteristics and page sizes. In addition, it is found that reducing the miss rate by the prefetching scheme reduces the total miss penalty and bus traffics in software-managed TLBs.