1. A method for concurrent workload simulation for application performance testing, the method comprising: loading a list of recorded workloads for different tasks of a computing application under test in a workload simulator executing in memory by at least one processor of a host computer; grouping the recorded workloads by common task in a corresponding block and recording in each corresponding block, an order in which the recorded workloads for each task were recorded; generating loads for simulating performance of the computing application under test from the grouped workloads so as to require serial execution of workloads in a common block in order of appearance in the common block as recorded in the common block, but to allow concurrent execution of workloads in different blocks, wherein the generation of the loads can enforce ordering constraints of the different blocks; setting a synchronization point amongst the blocks; and, during generation of the loads, requiring all workloads in blocks appearing before the synchronization point to execute in an order of appearance if in a same block, but to execute concurrently in parallel if in different block, before permitting execution of workloads of blocks appearing subsequent to the synchronization point.