A comprehensive scheduler for asymmetric multicore systems

Symmetric-ISA (instruction set architecture) asymmetric-performance multicore processors were shown to deliver higher performance per watt and area for applications with diverse architectural requirements, and so it is likely that future multicore processors will combine a few fast cores characterized by complex pipelines, high clock frequency, high area requirements and power consumption, and many slow ones, characterized by simple pipelines, low clock frequency, low area requirements and power consumption. Asymmetric multicore processors (AMP) derive their efficiency from core specialization. Efficiency specialization ensures that fast cores are used for "CPU-intensive" applications, which efficiently utilize these cores' "expensive" features, while slow cores would be used for "memory-intensive" applications, which utilize fast cores inefficiently. TLP (thread-level parallelism) specialization ensures that fast cores are used to accelerate sequential phases of parallel applications, while leaving slow cores for energy-efficient execution of parallel phases. Specialization is effected by an asymmetry-aware thread scheduler, which maps threads to cores in consideration of the properties of both. Previous asymmetry-aware schedulers employed one type of specialization (either efficiency or TLP), but not both. As a result, they were effective only for limited workload scenarios. We propose, implement, and evaluate CAMP, a Comprehensive AMP scheduler, which delivers both efficiency and TLP specialization. Furthermore, we propose a new light-weight technique for discovering which threads utilize fast cores most efficiently. Our evaluation in the OpenSolaris operating system demonstrates that CAMP accomplishes an efficient use of an AMP system for a variety of workloads, while existing asymmetry-aware schedulers were effective only in limited scenarios.