How to identify a bottleneck?

Overview

Questions

• How can I find the bottlenecks in a job at hand?

Objectives

After completing this episode, participants should be able to …

• Name typical performance issues.
• Determine if their job is affected by one of these issues.

How to identify a bottleneck?

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Key Points

• General advice on the workflow
• Performance reports may provide an automated summary with recommendations
• Performance metrics can be categorized by the underlying hardware, e.g. CPU, memory, I/O, accelerators.
• Bottlenecks can appear by metrics being saturated at the physical limits of the hardware or indirectly by other metrics being far from what the physical limits are.
• Interpreting bottlenecks is closely related to what the application is supposed to do.
• Relative measurements (baseline vs. change)
  • system is quiescent, fixed CPU freq + affinity, warmups, …
  • Reproducibility -> link to git course?
• Scanning results for smoking guns
• Any best practices etc.