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Publications of SPCL
|H. Schweizer, M. Besta, T. Hoefler:|
|Evaluating the Cost of Atomic Operations on Modern Architectures|
(presented in San Francisco, CA, USA, ACM, Oct. 2015, Accepted at the 24th International Conference on Parallel Architectures and Compilation (PACT'15) )
AbstractAtomic operations (atomics) such as Compare-and-Swap (CAS) or Fetch-and-Add (FAA) are ubiquitous in parallel programming. Yet, performance of these operations has not been thoroughly analyzed, hindering the development and the reasoning of high performance codes. In this paper we establish an evaluation methodology, develop a performance model, and present a set of detailed benchmarks for latency and bandwidth of different atomics. We consider various state-of-the-art x86 architectures: Intel Haswell, Xeon Phi, Ivy Bridge, and AMD Bulldozer. The results unveil surprising performance relationships between the considered atomics and architectural properties such as the coherence state of the accessed cache lines. One key finding is that all the tested atomics have comparable latency and bandwidth even if they are characterized by different consensus numbers. Another insight is that the hardware implementation of atomics prevents any instruction-level parallelism even if there are no dependencies between the issued operations. Finally, we discuss solutions to the discovered performance issues in the analyzed architectures. Our analysis enables simpler and more effective parallel programming and accelerates data processing on various architectures deployed in both off-the-shelf machines and large compute systems.
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