Chip multicore processors (CMPs) have emerged as the dominant architecture choice for modern computing platforms and will most likely continue to be dominant well into the foreseeable future. As with any system, CMPs offer a unique set of challenges. Chief among them is the shared resource contention that results because CMP cores are not independent processors but rather share common resources among cores such as the last level cache (LLC). Shared resource contention can lead to severe and unpredictable performance impact on the threads running on the CMP. Conversely, CMPs offer tremendous opportunities for mulithreaded applications, which can take advantage of simultaneous thread execution as well as fast inter thread data sharing. Many solutions have been proposed to deal with the negative aspects of CMPs and take advantage of the positive. This survey focuses on the subset of these solutions that exclusively make use of OS thread-level scheduling to achieve their goals. These solutions are particularly attractive as they require no changes to hardware and minimal or no changes to the OS. The OS scheduler has expanded well beyond its original role of time-multiplexing threads on a single core into a complex and effective resource manager. This article surveys a multitude of new and exciting work that explores the diverse new roles the OS scheduler can successfully take on.

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Asymmetric multicore processors (AMPs) consist of cores with the same ISA (instruction-set architecture), but different microarchitectural features, speed, and power consumption. Because cores with more complex features and higher speed typically use more area and consume more energy relative to simpler and slower cores, we must use these cores for running applications that experience significant performance improvements from using those features. Having cores of different types in a single system allows optimizing the performance/energy trade-off. To deliver this potential to unmodified applications, the OS scheduler must map threads to cores in consideration of the properties of both. Our work describes a Comprehensive scheduler for Asymmetric Multicore Processors (CAMP) that addresses shortcomings of previous asymmetryaware schedulers. First, previous schedulers catered to only one kind of workload properties that are crucial for scheduling on AMPs; either efficiency or thread-level parallelism (TLP), but not both. CAMP overcomes this limitation showing how using both efficiency and TLP in synergy in a single scheduling algorithm can improve performance. Second, most existing schedulers relying on models for estimating how much faster a thread executes on a "fast" vs. "slow" core (i.e., the speedup factor) were specifically designed for AMP systems where cores differ only in clock frequency. However, more realistic AMP systems include cores that differ more significantly in their features. To demonstrate the effectiveness of CAMP on more realistic scenarios, we augmented the CAMP scheduler with a model that predicts the speedup factor on a real AMP prototype that closely matches future asymmetric systems.

Abstract-The widespread usage of the discrete wavelet transform (DWT) has motivated the development of fast DWT algorithms and their tuning on all sorts of computer systems. Several studies have compared the performance of the most popular schemes, known as Filter Bank Scheme (FBS) and Lifting Scheme (LS), and have always concluded that LS is the most efficient option. However, there is no such study on streaming processors such as modern Graphics Processing Units (GPUs). Current trends have transformed these devices into powerful stream processors with enough flexibility to perform intensive and complex floating-point calculations. The opportunities opened up by these platforms, as well as the growing popularity of the DWT within the computer graphics field, make a new performance comparison of great practical interest. Our study indicates that FBS outperforms LS in current-generation GPUs. In our experiments, the actual FBS gains range between 10 percent and 140 percent, depending on the problem size and the type and length of the wavelet filter. Moreover, design trends suggest higher gains in future-generation GPUs.

The causative viral agent of a lethal rabbit hemorrhagic disease has been purified and characterized. In negative-stained preparations, the virions were icosahedral, measured 27 to 35 nm in diameter, were without an envelope, and showed 10 peripheral cup-shaped depressions. The major structural protein was 60 kilodaltons, which constitutes a unique characteristic of the Caliciviridae.

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