Braids and fibers: Language constructs with architectural support for adaptive responses to memory latencies

Abstract

As processor speeds continue to increase at a much higher rate than memory speeds, memory latencies may soon approach a thousand processor cycles. As a result, the flat memory model that was made practical by deeply pipelined superscalar processors with multilevel caches will no longer be tenable. The most common approach to this problem is multithreading; however, multithreading requires either abundant independent applications or well-parallelized monolithic applications, and neither is easy to come by. We present high-level programming constructs called braids and fibers. The programming constructs facilitate the creation of programs that are partially ordered, in which the partial orders can be used to support adaptive responses to memory access latencies. Braiding is simpler than parallelizing, while yielding many of the same benefits. We show how the programming constructs can be effectively supported with simple instruction set architecture extensions and microarchitectural enhancements. We have developed braided versions of a number of important algorithms. The braided code is easy to understand at the source level and can be translated into highly efficient instructions using our architecture extensions. © Copyright 2006 by International Business Machines Corporation.