To improve the performance of a single application on Chip Multiprocessors (CMPs), the application must be split into threads which execute concurrently on multiple cores. In multi-threaded applications, critical sections are used to ensure that only one thread accesses shared data at any given time. Critical sections can serialize the execution of threads, which significantly reduces performance and scalability. This paper proposes Accelerated Critical Sections (ACS), a technique that leverages the high-performance core(s) of an Asymmetric Chip Multiprocessor (ACMP) to accelerate the execution of critical sections. In ACS, selected critical sections are executed by a high-performance core, which can execute the critical section faster than the other, smaller cores. Consequently, ACS reduces serialization: it lowers the likelihood of threads waiting for a critical section to finish. Our evaluation on a set of 12 critical-section-intensive workloads shows that ACS reduces the average execution time by 34% compared to an equal-area 32-core symmetric CMP and by 23% compared to an equal-area ACMP. Moreover, for 7 of the 12 workloads, ACS also increases scalability (i.e. the number of threads at which performance saturates).

Performance of multithreaded applications is limited by a variety of bottlenecks, e.g. critical sections, barriers and slow pipeline stages. These bottlenecks serialize execution, waste valuable execution cycles, and limit scalability of applications. This paper proposes Bottleneck Identification and Scheduling (BIS), a cooperative software-hardware mechanism to identify and accelerate the most critical bottlenecks. BIS identifies which bottlenecks are likely to reduce performance by measuring the number of cycles threads have to wait for each bottleneck, and accelerates those bottlenecks using one or more fast cores on an Asymmetric Chip MultiProcessor (ACMP). Unlike previous work that targets specific bottlenecks, BIS can identify and accelerate bottlenecks regardless of their type. We compare BIS to four previous approaches and show that it outperforms the best of them by 15% on average. BIS' performance improvement increases as the number of cores and the number of fast cores in the system increase.

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Extracting high performance from Chip Multiprocessors requires that the application be parallelized. A common software technique to parallelize loops is pipeline parallelism in which the programmer/compiler splits each loop iteration into stages and each stage runs on a certain number of cores. It is important to choose the number of cores for each stage carefully because the core-to-stage allocation determines performance and power consumption. Finding the best core-to-stage allocation for an application is challenging because the number of possible allocations is large, and the best allocation depends on the input set and machine configuration.This paper proposes Feedback-Directed Pipelining (FDP), a software framework that chooses the core-to-stage allocation at run-time. FDP first maximizes the performance of the workload and then saves power by reducing the number of active cores, without impacting performance. Our evaluation on a real SMP system with two Core2Quad processors (8 cores) shows that FDP provides an average speedup of 4.2x which is significantly higher than the 2.3x speedup obtained with a practical profile-based allocation. We also show that FDP is robust to changes in machine configuration and input set.

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Higher homologues of widely reported C(86) isoprenoid diglycerol tetraether lipid cores, containing 0-6 cyclopentyl rings, have been identified in (hyper)thermophilic archaea, representing up to 21% of total tetraether lipids in the cells. Liquid chromatography-tandem mass spectrometry confirms that the additional carbon atoms in the C(87-88) homologues are located in the etherified chains. Structures identified include dialkyl and monoalkyl ('H-shaped') tetraethers containing C(40-42) or C(81-82) hydrocarbons, respectively, many representing novel compounds. Gas chromatography-mass spectrometric analysis of hydrocarbons released from the lipid cores by ether cleavage suggests that the C(40) chains are biphytanes and the C(41) chains 13-methylbiphytanes. Multiple isomers, having different chain combinations, were recognised among the dialkyl lipids. Methylated tetraethers are produced by Methanothermobacter thermautotrophicus in varying proportions depending on growth conditions, suggesting that methylation may be an adaptive mechanism to regulate cellular function. The detection of methylated lipids in Pyrobaculum sp. AQ1.S2 and Sulfolobus acidocaldarius represents the first reported occurrences in Crenarchaeota. Soils and aquatic sediments from geographically distinct mesotemperate environments that were screened for homologues contained monomethylated tetraethers, with di- and trimethylated structures being detected occasionally. The structural diversity and range of occurrences of the C(87-89) tetraethers highlight their potential as complementary biomarkers for archaea in natural environments.