Extracting SMP parallelism for dense linear algebra algorithms from high-level specifications

Abstract

We show how to exploit high-level information, available as part of the derivation of provably correct algorithms, so that SMP parallelism can be systematically identified. Recent research has shown that loop-based dense linear algebra algorithms can be systematically derived from the mathematical specification of the operation. Fundamental to the methodology is the determination of loop-invariants (in the sense of Dijkstra and Hoare) from which correct loops can be systematically derived. We show how the high-level specification of the operation together with these loop-invariants can be exploited to detect the independence of loop iterations. This in turn then allows a Workqueuing Model to be used to implement and parallelize the algorithms using a feature proposed for OpenMP 3.0, task queues. Although performance is not the main feature of this paper, performance is reported on a 4 CPU Itanium2 server for a concrete example, the symmetric rank-k update operation.