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and have different power characteristics. Using the same ISA on all cores means running the same binary on all cores without the need to compile code with a different compiler for each core type. This stands in contrast to heterogeneous-ISA systems, such as IBM's Cell or Intel's Larrabee, where the cores expose different ISAs, so the code must be compiled separately for each core type. Heterogeneous-ISA systems are not the focus of this article.A typical AMP consists of several fast and powerful cores (high clock frequency, complex out-of-order pipeline, and high power consumption) and a large number of slower low-power cores (low clock frequency, simple pipeline, and low power consumption). Complex and powerful cores are good for running single-threaded sequential applications because these applications cannot accelerate their performance by spreading the computation across multiple simple cores. Abundant simple cores, on the other hand, are good for running highly scalable parallel applications.Because of performance/power trade-offs between complex and simple cores, it turns out to be much more efficient to run a parallel application on a large number of simple cores than on a smaller number of complex cores that consume the same power or fit into the same area. In a similar vein, complex and powerful cores are good for running CPU-intensive applications that effectively use those processors' advanced microarchitectural features, such as out-of-order super-scalar pipelines, advanced branch prediction facilities, and replicated functional units. At the same time, simple and slow cores deliver a better trade-off between energy consumption and performance for memory-intensive applications that spend a majority of their execution time fetching data from off-chip memory and stalling the processor.A symmetric multicore processor (SMP) includes the cores of only one type: either the complex and powerful ones, as in the Intel Xeon or AMD Opteron processors, or the simple and in CoMPutinG SySteMS, a CPU is usually one of the largest consumers of energy. For this reason reducing CPU power consumption has been a hot topic in the past few years in both the academic community and the industry. In the quest to create more powerefficient CPUs, several researchers proposed an asymmetric multicore architecture that promises to save a significant amount of power while delivering similar performance as conventional symmetric multicore processors.An asymmetric multicore processor (AMP) consists of cores that use the same instruction set architecture (ISA) but deliver different performance

Future heterogeneous single-ISA multicore processors will have an edge in potential performance per watt over comparable homogeneous processors. To fully tap into that potential, the OS scheduler needs to be heterogeneity-aware, so it can match jobs to cores according to characteristics of both. We propose a Heterogeneity-Aware Signature-Supported scheduling algorithm that does the matching using per-thread architectural signatures, which are compact summaries of threads' architectural properties collected offline. The resulting algorithm does not rely on dynamic profiling, and is comparatively simple and scalable. We implemented HASS in OpenSolaris, and achieved average workload speedups of up to 13%, matching best static assignment, achievable only by an oracle. We have also implemented a dynamic IPC-driven algorithm proposed earlier that relies on online profiling. We found that the complexity, load imbalance and associated performance degradation resulting from dynamic profiling are significant challenges to using this algorithm successfully. As a result it failed to deliver expected performance gains and to outperform HASS.

In computing systems, a CPU is usually one of the largest consumers of energy. For this reason, reducing CPU power consumption has been a hot topic in the past few years in both the academic community and the industry. In the quest to create more power-efficient CPUs, several researchers have proposed an asymmetric multicore architecture that promises to save a significant amount of power while delivering similar performance to conventional symmetric multicore processors. An AMP (asymmetric multicore processor) consists of cores that use the same ISA (instruction set architecture) but deliver different performance and have different power characteristics. Using the same ISA on all cores means that you can run the same binary on all cores and not have to compile your code with a different compiler for each core type. This stands in contrast to heterogeneous-ISA systems, such as IBM's Cell or Intel's Larrabee, where the cores expose different ISAs, so the code must be compiled separately for each core type. Heterogeneous-ISA systems are not the focus of this article. A typical AMP consists of several fast and powerful cores (high clock frequency, complex out-oforder pipeline, high power consumption) and a large number of slower low-power cores (low clock frequency, simple pipeline, low power consumption). Complex and powerful cores are good for running single-threaded sequential applications, because these applications cannot accelerate their performance by spreading the computation across multiple simple cores. Abundant simple cores, on the other hand, are good for running highly scalable parallel applications. Because of performance/power trade-offs between complex and simple cores, it turns out to be a lot more efficient to run a parallel application on a large number of simple cores than on a smaller number of complex cores that consume the same power or fit into the same area. In a similar vein, complex and powerful cores are good for running CPU-intensive applications that effectively use those processors' advanced microarchitectural features, such as out-of-order super-scalar pipelines, advanced branch prediction facilities, and replicated functional units. At the same time, simple and slow cores deliver a better trade-off between energy consumption and performance for memorybound applications that spend a majority of their execution time fetching data from off-chip memory and stalling the processor. An SMP (symmetric multicore processor) includes cores of only one type: either the complex and powerful ones, as in the Intel Xeon and AMD Opteron processors, or the simple and lower-power ones, as in Sun's Niagara. So in terms of providing the optimal performance/power, an SMP is ideally suited for some applications but not all. Having cores of different types in a single processor enables optimizing performance per watt for a wider range of workloads. Having cores of different

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