Scalable Comparative Visualization of Ensembles of Call Graphs

TL;DR

This paper introduces an enhanced visualization tool called CallFlow for exploring ensembles of call graphs, combining Sankey diagrams and box plots to analyze structural differences and performance variability in large-scale parallel code performance profiles.

Contribution

The paper presents a novel visualization method, ensemble-Sankey, and an interactive interface for analyzing multiple call graphs simultaneously, improving understanding of performance variability and structural differences.

Findings

Effective visualization of large call graph ensembles demonstrated

Facilitates identification of performance bottlenecks and structural differences

Case studies show improved analysis capabilities

Abstract

Optimizing the performance of large-scale parallel codes is critical for efficient utilization of computing resources. Code developers often explore various execution parameters, such as hardware configurations, system software choices, and application parameters, and are interested in detecting and understanding bottlenecks in different executions. They often collect hierarchical performance profiles represented as call graphs, which combine performance metrics with their execution contexts. The crucial task of exploring multiple call graphs together is tedious and challenging because of the many structural differences in the execution contexts and significant variability in the collected performance metrics (e.g., execution runtime). In this paper, we present an enhanced version of CallFlow to support the exploration of ensembles of call graphs using new types of visualizations, analysis, graph operations, and features. We introduce ensemble-Sankey, a new visual design that combines the strengths of resource-flow (Sankey) and box-plot visualization techniques. Whereas the resource-flow visualization can easily and intuitively describe the graphical nature of the call graph, the box plots overlaid on the nodes of Sankey convey the performance variability within the ensemble. Our interactive visual interface provides linked views to help explore ensembles of call graphs, e.g., by facilitating the analysis of structural differences, and identifying similar or distinct call graphs. We demonstrate the effectiveness and usefulness of our design through case studies on large-scale parallel codes.