Section: New Results

On Characterizing the Data Access Complexity of Programs

Participants : Venmugil Elango [OSU] , Fabrice Rastello, Louis-Noël Pouchet [UCLA] , J. Ramanujam [LSU] , P. Sadayappan [OSU] .

Technology trends will cause data movement to account for the majority of energy expenditure and execution time on emerging computers. Therefore, computational complexity will no longer be a sufficient metric for comparing algorithms, and a fundamental characterization of data access complexity will be increasingly important. The problem of developing lower bounds for data access complexity has been modeled using the formalism of Hong & Kung's red/blue pebble game for computational directed acyclic graphs (CDAGs). However, previously developed approaches to lower bounds analysis for the red/blue pebble game are very limited in effectiveness when applied to CDAGs of real programs, with computations comprised of multiple sub-computations with differing DAG structure. We address this problem by developing an approach for effectively composing lower bounds based on graph decomposition. We also develop a static analysis algorithm to derive the asymptotic data-access lower bounds of programs, as a function of the problem size and cache size.

This work is the fruit of the collaboration  8.1 with OSU and is to be presented at ACM POPL'15.