Detection of Strong Unstable Predicates in Distributed Programs

This paper discusses detection of global predicates in a distributed program. A run of a distributed program results in a set of sequential traces, one for each process. These traces may be combined to form many global sequences consistent with the single run of the program. A strong global predicate is true in a run if it is true for all global sequences consistent with the run. We present algorithms which detect if the given strong global predicate became true in a run of a distributed program. 1 Introduction Detection of global predicates is a fundamental problem in distributed computing. It arises in the designing, debugging and testing of distributed programs. Global predicates can be classified into two types - stable and unstable. A stable predicate is one which never turns false once it becomes true. An unstable predicate is one without such a property. Its value may alternate between true and false. Detection of stable predicates has been addressed in the literature by means ..

Detection of Weak Unstable Predicates in Distributed Programs

This paper discusses detection of global predicates in a distributed program. Earlier algorithms for detection of global predicates proposed by Chandy and Lamport work only for stable predicates. A predicate is stable if it does not turn false once it becomes true. Our algorithms detect even unstable predicates without excessive overhead. In the past, such predicates have been regarded as too difficult to detect. The predicates are specified using a logic described formally in this paper. We discuss detection of weak conjunctive predicates which are formed by conjunction of predicates local to processes in the system. Our detection methods will detect if such a predicate is true for any interleaving of events in the system, whether the predicate is stable or not. Also, any predicate which can be reduced to a set of weak conjunctive predicates is detectable. This class of predicates captures many global predicates that are of interest to a programmer. The message complexity of our algor..

Understanding and Mitigating Multicore Performance Issues on the AMD Opteron Architecture

Over the past 15 years, microprocessor performance has doubled approximately every 18 months through increased clock rates and processing efficiency. In the past few years, clock frequency growth has stalled, and microprocessor manufacturers such as AMD have moved towards doubling the number of cores every 18 months in order to maintain historical growth rates in chip performance. This document investigates the ramifications of multicore processor technology on the new Cray XT4? systems based on AMD processor technology. We begin by walking through the AMD single-core and dual-core and upcoming quad-core processor architectures. This is followed by a discussion of methods for collecting performance counter data to understand code performance on the Cray XT3? and XT4? systems. We then use the performance counter data to analyze the impact of multicore processors on the performance of microbenchmarks such as STREAM, application kernels such as the NAS Parallel Benchmarks, and full application codes that comprise the NERSC-5 SSP benchmark suite. We explore compiler options and software optimization techniques that can mitigate the memory bandwidth contention that can reduce computing efficiency on multicore processors. The last section provides a case study of applying the dual-core optimizations to the NAS Parallel Benchmarks to dramatically improve their performance

Defining the molecular basis for the first potent and selective orthosteric agonists of the FFA2 free fatty acid receptor

Background: Understanding the function of FFA2 has been slowed by a lack of selective orthosteric ligands. Results: Residues within FFA2 that dictate the recognition and function of potent and selective orthosteric agonists are described. Conclusion: Key aspects of ligand interaction with the orthosteric binding pocket of FFA2 are defined. Significance: This work will be invaluable in future drug development at the FFA2 receptor