No abstract

We demonstrate the feasibility of undertaking performance evaluations for JVMs using: (1) a hybrid JVM/OS tool, such as async-profiler, (2) OS centric profiling and tracing tools based on Linux perf, and (3) the Extended Berkeley Packet Filter Tracing (eBPF) framework where we demonstrate the rationale behind the standard offwaketime tool, for analysing the causes of blocking latencies, and our own eBPF-based tool bcc-java, that relates changes in microarchitecture performance counter values to the execution of individual JVM and application threads at low overhead. The relative execution time overheads of the performance tools are illustrated for the DaCapo-bach-9.12 benchmarks with Open-JDK9 on an Intel Xeon E5-2690, running Ubuntu 16.04. Whereas sampling based tools can have up to 25% slowdown using 4kHz frequency, our tool bcc-java has a geometric mean of less than 5%. Only for the avrora benchmark, bcc-java has a significant overhead (37%) due to an unusually high number of futex system calls. Finally, we provide a discussion on the recommended approaches to solve specific performance use-case scenarios. CCS CONCEPTS • General and reference → Performance; • Software and its engineering → Virtual machines.

No abstract

The time reversal symmetry of the wave equation allows wave refocusing back at the source. However, this symmetry does not hold in lossy media. We present a new strategy to compensate wave amplitude losses due to attenuation. The strategy leverages the instantaneous time mirror (ITM) which generates reversed waves by a sudden disruption of the medium properties. We create a heterogeneous ITM whose disruption is unequal throughout the space to create waves of different amplitude. The time-reversed waves can then cope with different attenuation paths as typically seen in heterogeneous and lossy environments. We consider an environment with biological tissues and apply the strategy to a two-dimensional digital human phantom from the abdomen. A stronger disruption is introduced where forward waves suffer a history of higher attenuation, with a weaker disruption elsewhere. Computer simulations show heterogeneous ITM is a promising technique to improve time reversal refocusing in heterogeneous, lossy, and dispersive spaces.