The advent of Cloud computing as a new model of service provisioning in distributed systems, encourages researchers to investigate its benefits and drawbacks in executing scientific applications such as workflows. In this model, the users request for available services according to their desired Quality of Service, and they are charged on a pay-per-use basis. One of the most challenging problems in Clouds is workflow scheduling, i.e., the problem of satisfying the QoS of the user as well as minimizing the cost of workflow execution. In this paper, we propose a new QoS-based workflow scheduling algorithm based on a novel concept called Partial Critical Paths (PCP), which tries to minimize the cost of workflow execution while meeting a user-defined deadline. This algorithm recursively schedules the partial critical paths ending at previously scheduled tasks. The simulation results show that the performance of our algorithm is very promising.

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