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Emmanuel Jeannot, Esteban Meneses-Rojas, Guillaume Mercier, François Tessier and Gengbin Zheng

Communication and Topology-aware Load Balancing in Charm++ with TreeMatch

Abstract—Programming multicore or manycore architectures is a hard challenge particularly if one wants to fully take advantage of their computing power. Moreover, a hierarchical topology implies that communication performance is heterogeneous and this characteristic should also be exploited. We developed two load balancers for Charm++ that take into account both aspects depending on the fact that the application is compute-bound or communication-bound. This work is based on our TREEMATCH library that compute process placement in order to reduce an application communication cost based on the hardware topology. We show that the proposed load-balancing scheme manages to improve the execution times for the two classes of parallel applications.

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CALCioM: Mitigating I/O Interferences in HPC Systems through Cross-Application Coordination

Unmatched computation and storage performance in new HPC systems have led to a plethora of I/O optimizations ranging from application-side collective I/O to network and disk-level request scheduling on the file system side. As we deal with ever larger machines, the interference produced by multiple applications accessing a shared parallel file system in a concurrent manner become a major problem. Interference often breaks single-application I/O optimizations, dramatically degrading application I/O performance and, as a result, lowering machine wide efficiency.
This talk will focuse on CALCioM, a framework that aims to mitigate I/O interference through the dynamic selection of appropriate scheduling policies. CALCioM allows several applications running on a supercomputer to communicate and coordinate their I/O strategy in order to avoid interfering with one another. In this work, we examine four I/O strategies that can be accommodated in this framework: serializing, interrupting, interfering and coordinating. Experiments on Argonne’s BG/P Surveyor machine and on several clusters of the French Grid’5000 show how CALCioM can be used to efficiently and transparently improve the scheduling strategy between two otherwise interfering applications, given specified metrics of machine wide efficiency.

Babak Behzad

Taming Parallel I/O Complexity with Auto-Tuning

We present an auto-tuning system for optimizing I/O performance of HDF5 applications and demonstrate its value across platforms, applications, and at scale. The system uses genetic algorithms to search a large space of tunable parameters and to identify effective settings at all layers of the parallel I/O stack. The parameter settings are applied transparently by the auto-tuning system via dynamically intercepted HDF5 calls. To validate our auto-tuning system, we applied it to three I/O benchmarks (VPIC, VORPAL, and GCRM) that replicate the I/O activity of their respective applications. We tested the system with different weak-scaling configurations (128, 2048, and 4096 CPU cores) that generate 30 GB to 1 TB of data, and executed these configurations on diverse HPC platforms (Cray XE6, IBM BG/P, and Dell Cluster). In all cases, the auto-tuning framework identified tunable parameters that substantially improved write performance over default system settings. We consistently demonstrate I/O write speedups between 2x and 100x for test configurations.

Yves Robert, ENS Lyon, INRIA & Univ. Tenn. Knoxville

Assessing the impact of ABFT & Checkpoint composite strategies
 

Algorithm-specific fault tolerant approaches promise unparalleled scalability and performance in failure-prone environments. With the advances in the theoretical and practical understanding of algorithmic traits enabling such approaches, a growing number of frequently used algorithms (including all widely used factorization kernels) have been proven capable of such properties. These algorithms provide a temporal section of the execution when the data is protected by it's own intrinsic properties, and can be algorithmically recomputed without the need of checkpoints. However, while typical scientific applications spend a significant fraction of  their execution time in library calls that can be ABFT-protected, they interleave sections that are difficult or even impossible to protect with ABFT.  As a consequence, the only fault-tolerance approach that is currently used for these applications is  checkpoint/restart. In this talk, we propose a model and a simulator to investigate the behavior of a composite protocol,  that alternates  between ABFT and checkpoint/restart protection for effective protection of each phase of an iterative application composed of ABFT-aware and ABFT-unaware sections. We highlight this approach drastically increases the performance delivered by the system, especially at scale, by providing means to rarefy the checkpoints while simultaneously decreasing the volume of data needed to be saved in the checkpoints.