Characterizing the behavior of sparse algorithms on caches
Résumé
While there are many studies on the locality of dense codes, few deal with the locality of sparse codes. Because of indirect addressing sparse codes exhibit irregular patterns of references. In this paper, the behavior on cache of one of the most frequent primitives SpMxV (Sparse Matrix-Vector multiply) is analyzed. A model of its references is built and then performance bottlenecks of SpMxV are analyzed using model and simulations. Main parameters are identified and their role is explained and quantified. Then, this analysis is used to discuss optimizations of SpMxV. Moreover a blocking technique which takes into account the specifics of sparse codes is proposed.