Extreme scale computing: Modeling the impact of system noise in multi-core clustered systems

Seelam, Seetharami; Fong, Liana; Tantawi, Asser N.; Lewars, John; Divirgilio, John; Gildea, K.

doi:10.1016/j.jpdc.2013.01.016

Cited by 2 publications

(1 citation statement)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Here, a sensitive application is one in which an MPI synchronizing collective call (e.g., MPI_Barrier, MPI_Allreduce, MPI_Allgather, and so on) is called at least once per iteration in an iterative simulation or algorithm. Previous works() have shown that interference sources have potentially greater impact on applications with fine‐grained parallelism (i.e., applications with shorter per‐iteration intervals). For example, in Seelam et al, authors show that jitter can generate slowdowns as high as 8% for applications with computation intervals of 100 ms and over 16% of slowdowns for applications with 10‐ms computation intervals at 32 K CPUs.…”

Section: Importance Of Time Agreementmentioning

confidence: 99%

An evaluation of the state of time synchronization on leadership class supercomputers

Jones

Ostrouchov

Koenig

et al. 2017

Concurrency and Computation

View full text Add to dashboard Cite

SummaryWe present a detailed examination of time agreement characteristics for nodes within extreme-scale parallel computers. Using a software tool we introduce in this paper, we quantify attributes of clock skew among nodes in three representative high-performance computers sited at three national laboratories. Our measurements detail the statistical properties of time agreement among nodes and how time agreement drifts over typical application execution durations.We discuss the implications of our measurements, why the current state of the field is inadequate, and propose strategies to address observed shortcomings. KEYWORDSclock synchronization, large-scale systems, system software, time service INTRODUCTIONThe trend towards increasing node counts in high-performance computing (HPC) is motivating a move toward greater levels of concurrency in HPC systems. Today's software environment is now being called on to produce new solutions for emerging issues including managing system power, resilience, and performance characteristics. The distributed algorithms that underlie such services operate much more efficiently in the presence of tightly synchronized clocks. For example, tightly synchronized clocks benefit well-known gang scheduling techniques and complex consensus algorithms. To illustrate the point, such time synchronization enables more aggressive assumptions about communication and synchronization patterns, the removal of unnecessary locks, and a wide range of other applications. Clock-based techniques are already frequently deployed in cloud and data center distributed systems for precisely these reasons.We examined the time synchronization on some of the world's fastest and most powerful machines. These leadership-class systems employ high-end hardware connected by an extremely low-latency, low-jitter, interconnect in a carefully controlled environment, in contrast to widely distributed cloud-based systems based on commodity hardware and networks. Because of this, we assumed that these systems would have more stable, predictable hardware clocks, and close base time agreement using only standard time synchronization systems like Network Time Protocol (NTP). We did not believe that the complex hardware and software techniques used to provide time synchronization in wide-area systems would be necessary in leadership systems.Our results demonstrate that the actual time uncertainty for leadership-class machines is often unexpectedly large, in some cases over 600 milliseconds despite network latencies of less than two microseconds. Building on this, we set out to thoroughly quantify the magnitude of the time synchronization challenge in leadership-class systems. This study shows that the current time protocol in use, NTP, is not suitable for providing the level of time synchronization necessary for important system software tasks such as coordinated scheduling. Based on this, we conclude

show abstract

Section: Importance Of Time Agreementmentioning

confidence: 99%