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Amdahl’s law implies that even small sequential bottlenecks can seriously limit the scalability of multi-threaded programs. To achieve scalability, developers must painstakingly identify sequential bottlenecks in their program and eliminate these bottlenecks by either changing synchronization strategies or rearchitecting and rewriting any code with sequential bot- tlenecks. This can require significant effort by the developer to find and understand how to fix sequential bottlenecks. To address the issue, we bring a new tool, information flow, to the problem of understanding sequential bottlenecks. In- formation flow can help developers understand whether a bottleneck is fundamental to the computation, or merely an artifact of the implementation. First, our strategy tracks memory access conflicts to find over-synchronized applications where redesigning the syn- chronization strategy on the existing implementation can improve performance. Then, information flow analysis finds optimization opportunities where changing the existing im- plementation can improve performance of applications that have bottlenecks due to unnecessary memory access con- flicts. We implemented this in FlowProf. We have evaluated FlowProf on a set of multi-threaded Java applications where the generated optimization insights achieve performance gains of up to 58%.