Redesigning a tagless access buffer to require minimal ISA changes
Paper in proceedings, 2016

Energy efficiency is a first-order design goal for nearly all classes of processors, but it is particularly important in mobile and embedded systems. Data caches in such systems account for a large portion of the processor's energy usage, and thus techniques to improve the energy efficiency of the cache hierarchy are likely to have high impact. Our prior work reduced data cache energy via a tagless access buffer (TAB) that sits at the top of the cache hierarchy. Strided memory references are redirected from the level-one data cache (L1D) to the smaller, more energy-efficient TAB. These references need not access the data translation lookaside buffer (DTLB), and they can avoid unnecessary transfers from lower levels of the memory hierarchy. The original TAB implementation requires changing the immediate field of load and store instructions, necessitating substantial ISA modifications. Here we present a new TAB design that requires minimal instruction set changes, gives software more explicit control over TAB resource management, and remains compatible with legacy (non-TAB) code. With a line size of 32 bytes, a four-line TAB can eliminate 31% of L1D accesses, on average. Together, the new TAB, L1D, and DTLB use 22% less energy than a TAB-less hierarchy, and the TAB system decreases execution time by 1.7%.

memory hierarchy

energy efficiency

strided access

Author

Carlos Sanchez

Florida State University

Peter Gavin

Florida State University

Daniel Moreau

Chalmers, Computer Science and Engineering (Chalmers), Computer Engineering (Chalmers)

Magnus Själander

Uppsala University

Norges teknisk-naturvitenskapelige universitet

David Whalley

Florida State University

Per Larsson-Edefors

Chalmers, Computer Science and Engineering (Chalmers), Computer Engineering (Chalmers)

Sally A McKee

Chalmers, Computer Science and Engineering (Chalmers), Computer Engineering (Chalmers)

Proceedings of the International Conference on Compilers, Architectures and Synthesis for Embedded Systems, CASES 2016

Article number 2968504- 2968504

Areas of Advance

Information and Communication Technology

Subject Categories

Computer Systems

DOI

10.1145/2968455.2968504

ISBN

978-1-4503-2138-9