Memory hierarchy considerations for fast transpose and bit-reversals

Abstract

This paper explores the interplay between algorithm design and a computer's memory hierarchy. Matrix transpose and the bit-reversal reordering are important scientific subroutines which often exhibit severe performance degradation due to cache and TLB associativity problems. We give lower bounds that show for typical memory hierarchy designs, extra data movement is unavoidable. We also prescribe characteristics of various levels of the memory hierarchy needed to perform efficient bit-reversals. Insight gained from our analysis leads to the design of a near optimal bit-reversal algorithm. This Cache Optimal Bit Reverse Algorithm (COBRA) is implemented on the Digital Alpha 21164, Sun Ultrasparc 2, and IBM Power2. We show that COBRA is near optimal with respect to execution time on these machines and performs much better than previous best known algorithms.