As the computing industry enters the multicore era, exponential growth in the number of transistors on a chip continues to present challenges and opportunities for computer architects and system designers. We examine one emerging issue in particular: that of dynamic heterogeneity, which can arise, even among physically homogeneous cores, from changing reliability, power, or thermal conditions, different cache and TLB contents, or changing resource configurations. This heterogeneity results in a constantly varying pool of hardware resources, which greatly complicates software's traditional task of assigning computation to cores. In part to address dynamic heterogeneity, we argue that hardware should take a more active role in the management of its computation resources. We propose hardware techniques to virtualize the cores of a multicore processor, allowing hardware to flexibly reassign the virtual processors that are exposed, even to a single operating system, to any subset of the physical cores. We show that multicore virtualization operates with minimal overhead, and that it enables several novel resource management applications for improving both performance and reliability.
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