Hot spot (computer programming)

Abstract: When a large number of processors try to access a common variable, referred to as hot-spot accesses in [6], not only can the resulting memory contention seriously degrade performance, but it can also cause tree saturation in the interconnection network which blocks both hot and regular requests alike. It is shown in [6] that even if only a small percentage of all requests are to a hot-spot, these requests can cause very serious performances problems, and networks that do the necessary combining of requests are suggested to keep the interconnection network and memory contention from becoming a bottleneck.

Abstract: The combining of messages within a multistage switching network has been proposed to reduce memory contention in highly parallel shared-memory multiprocessors, especially for shared lock and synchronization data. A quantitative investigation of the performance impact of such contention and the effectiveness of combining in reducing this impact is reported. The effect of a nonuniform traffic pattern consisting of a single hot spot of higher access rate superimposed on a background of uniform traffic was investigated. The potential degradation due to even moderate hot spot traffic was found to be very significant, severely degrading all memory access, not just access to shared lock locations, due to an effect the authors call tree saturation. The technique of message combining was found to be an effective means of eliminating this problem if it arises due to lock or synchronization contention.

Abstract: Plasmonic nanostructures have tremendous potential to be applied in photocatalytic CO2 reduction, since their localized surface plasmon resonance can collect low‐energy‐photons to derive energetic “hot electrons” for reducing the CO2 activation‐barrier. However, the hot electron‐driven CO2 reduction is usually limited by poor efficiency and low selectivity for producing kinetically unfavorable hydrocarbons. Here, a new idea of plasmonic active “hot spot”‐confined photocatalysis is proposed to overcome this drawback. W18O49 nanowires on the outer surface of Au nanoparticles‐embedded TiO2 electrospun nanofibers are assembled to obtain lots of Au/TiO2/W18O49 sandwich‐like substructures in the formed plasmonic heterostructure. The short distance (< 10 nm) between Au and adjacent W18O49 can induce an intense plasmon‐coupling to form the active “hot spots” in the substructures. These active “hot spots” are capable of not only gathering the incident light to enhance “hot electrons” generation and migration, but also capturing protons and CO through the dual‐hetero‐active‐sites (Au‐O‐Ti and W‐O‐Ti) at the Au/TiO2/W18O49 interface, as evidenced by systematic experiments and simulation analyses. Thus, during photocatalytic CO2 reduction at 43± 2 °C, these active “hot spots” enriched in the well‐designed Au/TiO2/W18O49 plasmonic heterostructure can synergistically confine the hot‐electron, proton, and CO intermediates for resulting in the CH4 and CO production‐rates at ≈35.55 and ≈2.57 µmol g−1 h−1, respectively, and the CH4‐product selectivity at ≈93.3%.

Abstract: This paper presents a novel hardware-based approach for identifying, profiling, and monitoring hot spots in order to support runtime optimization of general purpose programs. The proposed approach consists of a set of tightly coupled hardware tables and control logic modules that are placed in the retirement stage of a processor pipeline removed from the critical path. The features of the proposed design include rapid detection of program hot spots after changes in execution behavior, runtime-tunable selection criteria for hot spot detection, and negligible overhead during application execution. Experiments using several SPEC95 benchmarks, as well as several large WindowsNT applications, demonstrate the promise of the proposed design.