We examine the performance of the in-situ data exploration framework based on the in-situ Particle Based Volume Rendering (In-Situ PBVR) on the latest many-core platform. In-Situ PBVR converts extreme scale volume data into small rendering primitive particle data via parallel MonteCarlo sampling without costly visibility ordering. This feature avoids severe bottlenecks such as limited memory size per node and significant performance gap between computation and inter-node communication. In addition, remote in-situ data exploration is enabled by asynchronous file-based control sequences, which transfer the small particle data to client PCs, generate view-independent volume rendering images on client PCs, and change visualization parameters at runtime. In-Situ PBVR shows excellent strong scaling with low memory usage up to ∼ 100k cores on the Oakforest-PACS, which consists of 8,208 Intel Xeon Phi7250 (Knights Landing) processors. This performance is compatible with the remote in-situ data exploration capability.Keywords: in-situ visualization, volume rendering, runtime steering, strong scaling, performance evaluation.
IntroductionRecent advances in HPC technology enabled extreme scale simulations at several tens of Peta-FLOPS, while the performance gap between computation and data I/O is enhanced. Because of this severe I/O bottleneck, data handling procedures such as "data output from simulations to storage" and "data input from storage to visualization applications" are becoming very costly, and conventional post processing visualization strategies often fail. In-situ visualization is one of promising solutions to this issue. In this approach, the I/O bottleneck is avoided by combining simulations and visualization applications to visualize simulation data at runtime on the same computing nodes. This requires extreme scale parallel visualization with high scalability at the same level as the simulations.Computational fluid dynamics (CFD) applications are widely used in various science and engineering fields, and are expected to be one of major applications on future exa-scale systems. Although variety of scientific visualization methods have been developed for CFD applications, visualization methods applicable to massively parallel processing of extreme scale volume data are still limited. Therefore, volume rendering methods for in-situ approaches should be carefully selected from the viewpoint of massively parallel processing and flexible visual analytics. Volume rendering is one of scalable visualization methods, which are suitable especially for CFD applications. In addition, in Ref. [4], it was shown that the volume rendering makes visual analytics flexible by extending the definition of transfer functions (TFs) into multi-dimension. Multi-dimensional transfer functions (MDTFs) generate not only three dimensional (3D) volume rendering, but also iso-surfaces, slice planes, image cropping, and image composition.Another important requirement is interactivity of in-situ visualization. In the conventional in-situ ...