Embedded platforms are resource-constrained systems in which performance and memory requirements of executed code are of critical importance. However, standard techniques such as full just-in-time(JIT) compilation and/or adaptive optimization (AO) may not be appropriate for this type of systems due to memory and compilation overheads.The research presented in this paper proposes a technique that combines some of the main benefits of JIT compilation, superoperators(SOs) and profile-guided optimization, in order to deliver a lightweight Java bytecode compilation system, targeted for resource-constrained environments, that achieves runtime performance similar to that of state-of-the-art JIT/AO systems, while having a minimal impact on runtime memory consumption. The key ideas are to use profiler-selected, extended bytecode basic blocks as superoperators (new bytecode instructions) and to perform few, but very targeted, JIT/AO-like optimizations at compile time only on the superoperators' bytecode, as directed by compilation "hints" encoded as annotations. As such, our system achieves competitive performance to a JIT/AO system, but with a much lower impact on runtime memory consumption. Moreover, it is shown that our proposed system can further improve program performance by selectively inlining method calls embedded in the chosen superoperators, as directed by runtime profiling data and with minimal impact on classfile size.For experimental evaluation, we developed three Virtual Machines(VMs) that employ the ideas presented above. The customized VMs are first compared (w.r.t. runtime performance) to a simple, fast-to-develop VM (baseline) and then to a VM that employs JIT/AO. Our best-performing system attains speedups ranging from a factor of 1.52 to a factor of 3.07, w.r.t. to the baseline VM. When compared to a state-of-the-art JIT/AO VM, our proposed system performs better for three of the benchmarks and worse by less than a factor of 2 for three others. But our SO-extended VM outperforms the JIT/AO system by a factor of 16, on average, w.r.t. runtime memory consumption.
Energy consumption is one of the most important issues in resource-constrained embedded systems. Many such systems run Java-based applications due to Java's architecture-independent format (bytecode). Standard techniques for executing bytecode programs, e.g. interpretation or just-in-time compilation, have performance or memory issues that make them unsuitable for resource-constrained embedded systems. A superoperator-extended, lightweight Java Virtual Machine (JVM) can be used in resource-constrained embedded systems to improve performance and reduce memory consumption. This paper shows that such a JVM also significantly reduces energy consumption. This is due primarily to a considerable reduction in the number of memory accesses and thus in energy consumption in the instruction and data TLBs and caches and, in most cases, in DRAM energy consumption. Since the fraction of processor energy dissipated in these units is approximately 60%, the energy savings achieved are significant. The paper evaluates the number of load, store, and computational instructions eliminated by the use of proposed superoperators as compared to a simple interpreter on a set of embedded benchmarks. Using cache and DRAM per access energy we estimate the total processor/DRAM energy saved by using our JVM. Our results show that with 32KB caches the reduction in energy consumption ranges from 40% to 60% of the overall processor, plus DRAM energy. Even higher savings may be achieved with smaller caches and increased access to DRAM as DRAM access energy is fairly high.
OBJECTIVES. Reviewing the literature data related to Lindsay – Hemenway syndrome.MATERIAL AND METHODS. We searched PubMed and Google Scholar with the key words of “Lindsay-Hemenway syndrome”, “benign positional vertigo”, “vestibular rehabilitation”RESULTS. Lindsay-Hemenway syndrome is characterized by an association between vestibular neuronitis and BPPV. The specificity of the syndrome consists in the existence of an initial episode of acute vestibular neuropathy manifested by intense vertigo and nystagmus, followed in a variable time frame by episodes of posterior canal BPPV. The treatment of the syndrome consists in a combination of otolith repositioning manoeuvres and vestibular rehabilitation therapy. The physicians involved in treating patients with vestibular disorders should be aware of the existence of this syndrome in order to diagnose and treat the patients accordingly.CONCLUSION. The Lindsay-Hemenway syndrome is a challenge for the physician. In order to establish a diagnosis, a careful investigation of clinical history and objective examination are needed. The clinician should take into consideration the presence of a sudden vertigo without deafness followed by postural nystagmus, and unilateral labyrinthine hyporeflexia or absence of reflectivity. For a successful therapeutic approach, we should be able to combine manoeuvres of repositioning for BPPV with an appropriate vestibular rehabilitation therapy in order to ensure a correct central compensation of the peripheral unilateral deficit.
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