5,178 research outputs found
Idle Period Propagation in Message-Passing Applications
Idle periods on different processes of Message Passing applications are
unavoidable. While the origin of idle periods on a single process is well
understood as the effect of system and architectural random delays, yet it is
unclear how these idle periods propagate from one process to another. It is
important to understand idle period propagation in Message Passing applications
as it allows application developers to design communication patterns avoiding
idle period propagation and the consequent performance degradation in their
applications. To understand idle period propagation, we introduce a methodology
to trace idle periods when a process is waiting for data from a remote delayed
process in MPI applications. We apply this technique in an MPI application that
solves the heat equation to study idle period propagation on three different
systems. We confirm that idle periods move between processes in the form of
waves and that there are different stages in idle period propagation. Our
methodology enables us to identify a self-synchronization phenomenon that
occurs on two systems where some processes run slower than the other processes.Comment: 18th International Conference on High Performance Computing and
Communications, IEEE, 201
Propagation and Decay of Injected One-Off Delays on Clusters: A Case Study
Analytic, first-principles performance modeling of distributed-memory
applications is difficult due to a wide spectrum of random disturbances caused
by the application and the system. These disturbances (commonly called "noise")
destroy the assumptions of regularity that one usually employs when
constructing simple analytic models. Despite numerous efforts to quantify,
categorize, and reduce such effects, a comprehensive quantitative understanding
of their performance impact is not available, especially for long delays that
have global consequences for the parallel application. In this work, we
investigate various traces collected from synthetic benchmarks that mimic real
applications on simulated and real message-passing systems in order to pinpoint
the mechanisms behind delay propagation. We analyze the dependence of the
propagation speed of idle waves emanating from injected delays with respect to
the execution and communication properties of the application, study how such
delays decay under increased noise levels, and how they interact with each
other. We also show how fine-grained noise can make a system immune against the
adverse effects of propagating idle waves. Our results contribute to a better
understanding of the collective phenomena that manifest themselves in
distributed-memory parallel applications.Comment: 10 pages, 9 figures; title change
Implementation and evaluation of the sensornet protocol for Contiki
Sensornet Protocol (SP) is a link abstraction layer between the network layer and the link layer for sensor networks. SP was proposed as the core of a future-oriented sensor node architecture that allows flexible and optimized combination between multiple coexisting protocols. This thesis implements the SP sensornet protocol on the Contiki operating system in order to: evaluate the effectiveness of the original SP services; explore further requirements and implementation trade-offs uncovered by the original proposal. We analyze the original SP design and the TinyOS implementation of SP to design the Contiki port. We implement the data sending and receiving part of SP using Contiki processes, and the neighbor management part as a group of global routines. The evaluation consists of a single-hop traffic throughput test and a multihop convergecast test. Both tests are conducted using both simulation and experimentation. We conclude from the evaluation results that SP's link-level abstraction effectively improves modularity in protocol construction without sacrificing performance, and our SP implementation on Contiki lays a good foundation for future protocol innovations in wireless sensor networks
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