Dynamic Acceleration of Multithreaded Program Critical Paths in Near-Threshold Systems
MICROW '12 Proceedings of the 2012 45th Annual IEEE/ACM International Symposium on Microarchitecture Workshops
Criticality stacks: identifying critical threads in parallel programs using synchronization behavior
Proceedings of the 40th Annual International Symposium on Computer Architecture
Bottle graphs: visualizing scalability bottlenecks in multi-threaded applications
Proceedings of the 2013 ACM SIGPLAN international conference on Object oriented programming systems languages & applications
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Multi-threaded workloads typically show sublinear speedup on multi-core hardware, i.e., the achieved speedup is not proportional to the number of cores and threads. Sublinear scaling may have multiple causes, such as poorly scalable synchronization leading to spinning and/or yielding, and interference in shared resources such as the last-level cache (LLC) as well as the main memory subsystem. It is vital for programmers and processor designers to understand scaling bottlenecks in existing and emerging workloads in order to optimize application performance and design future hardware. In this paper, we propose the speedup stack, which quantifies the impact of the various scaling delimiters on multi-threaded application speedup in a single stack. We describe a mechanism for computing speedup stacks on a multi-core processor, and we find speedup stacks to be accurate within 5.1% on average for sixteen-threaded applications. We present several use cases: we discuss how speedup stacks can be used to identify scaling bottlenecks, classify benchmarks, optimize performance, and understand LLC performance.