Ruth Klundt

Red storm IO performance analysis

This paper will summarize an IO performance analysis effort performed on Sandia National Laboratories Red Storm platform. Our goal was to examine the IO system performance and identify problems or bottle-necks in any aspect of the IO sub-system. Our process examined the entire IO path from application to disk both in segments and as a whole. Our final analysis was performed at scale employing parallel IO access methods typically used in high performance computing applications.

A Case for Optimistic Coordination in HPC Storage Systems

High-performance computing (HPC) storage systems rely on access coordination to ensure that concurrent updates do not produce incoherent results. HPC storage systems typically employ pessimistic distributed locking to provide this functionality in cases where applications cannot perform their own coordination. This approach, however, introduces significant performance overhead and complicates fault handling. In this work we evaluate the viability of optimistic conditional storage operations as an alternative to distributed locking in HPC storage systems. We investigate design strategies and compare the two approaches in a prototype object storage system using a parallel read/modify/write benchmark. Our prototype illustrates that conditional operations can be easily integrated into distributed object storage systems and can outperform standard coordination primitives for simple update workloads. Our experiments show that conditional updates can achieve over two orders of magnitude higher performance than pessimistic locking for some parallel read/modify/write workloads.

Report of experiments and evidence for ASC L2 milestone 4467 : demonstration of a legacy application's path to exascale.

This report documents thirteen of Sandias contributions to the Computational Systems and Software Environment (CSSE) within the Advanced Simulation and Computing (ASC) program between fiscal years 2009 and 2012. It describes their impact on ASC applications. Most contributions are implemented in lower software levels allowing for application improvement without source code changes. Improvements are identified in such areas as reduced run time, characterizing power usage, and Input/Output (I/O). Other experiments are more forward looking, demonstrating potential bottlenecks using mini-application versions of the legacy codes and simulating their network activity on Exascale-class hardware. The purpose of this report is to prove that the team has completed milestone 4467-Demonstration of a Legacy Applications Path to Exascale. Cielo is expected to be the last capability system on which existing ASC codes can run without significant modifications. This assertion will be tested to determine where the breaking point is for an existing highly scalable application. The goal is to stretch the performance boundaries of the application by applying recent CSSE RD in areas such as resilience, power, I/O, visualization services, SMARTMAP, lightweight LWKs, virtualization, simulation, and feedback loops. Dedicated system time reservations and/or CCC allocations will be used to quantify the impact of system-level changes to extend the life and performance of the ASC code base. Finally, a simulation of anticipated exascale-class hardware will be performed using SST to supplement the calculations. Determine where the breaking point is for an existing highly scalable application: Chapter 15 presented the CSSE work that sought to identify the breaking point in two ASC legacy applications-Charon and CTH. Their mini-app versions were also employed to complete the task. There is no single breaking point as more than one issue was found with the two codes. The results were that applications can expect to encounter performance issues related to the computing environment, system software, and algorithms. Careful profiling of runtime performance will be needed to identify the source of an issue, in strong combination with knowledge of system software and application source code.

Detailed analysis of I/O traces for large scale applications

In this paper, we present a tool to extract I/O traces from very large applications running at full scale during their production runs. We analyze these traces to gain information about the application. We analyze the traces of three applications. The analysis showed that the I/O traces reveal much information about the application even without access to the source code. In particular, these I/O traces provide multiple indications towards the algorithmic nature of the application by observing the changes of data amount and I/O request distribution at the checkpoints. Adaptive Mesh Refinement (AMR) is one of the kind of algorithms that can exhibit such I/O behavior. This is the first study of I/O characteristics of unbalanced AMR-supported applications at scale. The key observations that we made in the trace were (1) Variation in aggregate data sizes across checkpoints for AMR and non-AMR applications, (2) Variation in the number of I/O calls by a client depending on the nature of the application, (3) Use of temporary files by applications and possible erroneous calls to I/O functions, (4) Variation in average data transfer size according as whether the application has AMR support or not, (5) Aggregation of I/O for processes executing on a single physical node through MPI-IO calls, and (6) Updates to specific data structures in the checkpoint file.

An extensible, portable, scalable cluster management software architecture

This paper describes an object-oriented software architecture for cluster integration and management that enables extensibility, portability, and scalability. This architecture has been successfully implemented and deployed on several large-scale production clusters at Sandia National Laboratories, the largest of which is currently 1861 nodes. This paper discusses the key features of the architecture that allow for easily extending the range of supported hardware devices and network topologies. We also describe in detail how the object-oriented structure that represents the hardware components can be used to implement scalable and portable cluster management tools.