Computing the Throughput of Probabilistic and Replicated Streaming Applications

In this paper. we investigate how to compute the throughput of probabilistic and replicated streaming applications. We are given (i) a streaming application whose dependence graph is a linear chain, (ii) a one-to-many mapping of the application onto a fully heterogeneous target. where a processor is assigned at most one application stage, but where a stage can be replicated onto a set of processors; and (iii) a set of I.I D (independent and Identically-Distributed) variables to model each computation and communication time in the mapping How can we compute the throughput of the application, i e the rate at which data sets can be processed? We consider two execution models, the Strict model where the actions of each processor are sequentializecl, and the Overlap model where a processor can compute and communicate in parallel The problem is easy when application stages are not replicated, i e, assigned to a single processor: in that case the throughput is dictated by the critical hardware resource However, when stages are replicated, i e, assigned to several processors, the problem becomes surprisingly complicated: even in the deterministic case, the optimal throughput may be lower than the smallest internal resource throughput To the best of our knowledge, the problem has never been considered in the probabilistic case The first main contribution of the paper is to provide a general method (although of exponential cost) to compute the throughput when mapping parameters follow I.I.D exponential laws. This general method is based upon the analysis of timed Petri nets deduced from the application mapping, it turns out that these Petri nets exhibit a regular structure in the Overlap model, thereby enabling to reduce the cost and provide a polynomial algorithm The second main contribution of the paper is to provide bounds for the throughput when stage parameters are arbitrary I I.D and N.B.U E (New Better than Used in Expectation) variables the throughput is bounded from below by the exponential case and bounded from above by the deterministic case