1 / 19

HOMME Trace Analysis

HOMME Trace Analysis. Fabrice Mizero Mentor: Dr. John Dennis Collaborators: Prof. Malathi Veeraraghavan ( University of Virginia) Prof. Robert D. Russell (University of New Hampshire) Qian Liu(University of New Hampshire) Aug 1, 2014. Roadmap. Motivation Background Methodology

meryl
Download Presentation

HOMME Trace Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HOMME Trace Analysis Fabrice Mizero Mentor: Dr. John Dennis Collaborators: Prof. MalathiVeeraraghavan (University of Virginia) Prof. Robert D. Russell (University of New Hampshire) Qian Liu(University of New Hampshire) Aug 1, 2014

  2. Roadmap Motivation Background Methodology Results Conclusion and Solutions Future Work

  3. Big Picture • Understanding the causes of poor performance of CESM on Yellowstone: a 5-step approach • Experimental execution and data collection • HOMME trace analysis • IBMgtSim: routing study • Network simulation • Integrated simulation

  4. 2-hop 4-hop 6-hop *Credit: Dr. John Dennis Zhengyang Liu

  5. Suspected Causes “…OS noise, shape of the allocated partition, and interference from other jobs.” Abhinav Bhatele et al. SC13 • Network Congestion • Head of Line Blocking • Credit-Based Flow Control • OS Jitter • Kernel Interrupts • Application Interference: • Self-Interference • Interference with others (Neighborhood Effect)

  6. Congestion • Head of Line Blocking (HOL) • Worst Case Scenario: • Congestion Spreading due to HOL Victim Flow H1 Out of Buffer Space!! H4 Out of Buffer Space!! S1 S2 H2 H5 Stuck!!! H3 H6 H7

  7. OS Jitter • Each compute node runs its own OS - RHEL • Interference caused by OS routines • Timer interrupts • OS Daemons • Hardware interrupts • Competition for CPU resources. • Example: Line Printer Daemon

  8. 3 Questions How does congestion impact network latency? How important is OS Jitter to network latency? What has a bigger impact to message latency: OS Jitter or Congestion?

  9. Experimental Set-Up • Congestion: • 2 Platforms • Jellystone: Non-production machine • Yellowstone: production machine • Different message sizes & Hop distance • OS Jitter: • Linux Transparent Huge Pages (THP)

  10. Methodology Clock Skew Correction Extrae Trace Collection Hop, Size Hop, Size Wilcoxon Rank Sum Test

  11. Extrae MPI-Isend Time Start End Tracing tool Developed at BSC Chronologic event, state, communications records One way communication delays – Visuals with Paraver

  12. Clock Skew Ideally, CAB= Cb(t2) – Ca(t1) Host B Cb(t2) Host A Ca(t1) In reality, Offset = Ca(t) – Cb(t) != 0 Skew = Ca’(t) - Cb’(t) != 0 • Same size, Same Hop-Count, host-pair level • Min delay: best approximation of offset • CAB(t) – min( CAB(t)) + minpingpong

  13. Statistical Methods • Wilcoxon Rank Sum Test: • Non-parametric significance test • Compare the means of two independent populations • Tests: • OS Jitter? • Jellystone: no THP <=> with THP • Congestion? • Yellowstone: 0-Hop delays  4-Hop Delays • Jellystone: THP  Yellowstone: THP

  14. Perfquery TOR Switch Credits? PortXmitWait No Yes Host A • Perfquery: IB performance counters query tool. • PortXmitWait: Port congestion monitoring • Credit-Based Flow control

  15. Results • How important is OS Jitter to network latency? • Jellystone::0-Hop::NoTHP vs. Jellystone::0-Hop::THP • Intranode communications delays with THP enabled are slower than without THP.

  16. Results • What has a bigger impact to message latency: OS Jitter or Congestion? • Comparing: Yellowstone: 0-Hop delays, 4-Hop delays • For all considered message sizes, intranode communications delays can outweigh internode delays

  17. Conclusion • OS Jitter can cause performance degradation or variability. • Inter-job interference can lead to application performance variability. Solutions • Congestion: • Dynamic Allocation of Virtual Lanes to redirect victim flows around congested ports. • OS Jitter: • Linux Tickless Kernel • MPI-3 for better control over share-memory communications.

  18. Future Work Further study on the Dynamic Virtual Lanes assignment solution Plan and collect new HOMME traces with PortXmitWait monitored and LSF Logs saved. Study intra-job interference More efficient algorithm of correcting Clock Skew

  19. Thank You Fabrice Mizero fm9ab@virginia.edu

More Related