Intel® Advisor User Guide

ID 766448
Date 7/13/2023
Public

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Loop Markup to Minimize Analysis Overhead

Issue

Running your target application with the Intel® Advisor can take substantially longer than running your target application without the Intel® Advisor. Depending on an accuracy level and analyses you choose for a perspective, different overhead is added to your application execution time. For example:

Runtime Overhead / Analysis

Survey

Characterization

Dependencies

MAP

Target application runtime with Intel® Advisor compared to runtime without Intel® Advisor

1.1x longer

2 - 55x longer

5 - 100x longer

5 - 20x longer

Solutions

Use the following techniques to skip uninteresting loops and analyze only interesting loops.

Select Loops by ID

Goal: Minimize collection overhead.

Applicable analyses: Characterization with Trip Counts and FLOP collection enabled, Dependencies, Memory Access Patterns.

Use when...

  • You want to perform a deeper analysis on only a few loops.

  • CLI environment: You cannot identify source file/line numbers, such as when you are analyzing a target application for which you do not have access to source code.

Note: In the commands below, make sure to replace the myApplication with your application executable path and name before executing a command. If your application requires additional command line options, add them after the executable name.

Prerequisites:

  1. Run a Survey analysis.

  2. advisor CLI environment: Identify the loop IDs for the loops of interest.

    advisor --report=survey --project-dir=./advi_results -- ./myApplication

    In the report, the first column is the loop IDs.

TIP:

Intel® Advisor reports tend to be very wide. Do one of the following to generate readable reports:

  • Set your console width appropriately to avoid line wrapping.

  • Pipe your report using the appropriate truncation command if you care only about the first few report columns.

After performing the prerequisites, do one of the following:

  • For Vectorization and CPU Roofline: Mark the loop(s) of interest by enabling the associated checkbox on the Survey Report.

    Then run a Characterization with Trip Counts and FLOP collection enabled, Dependencies, or Memory Access Patterns analysis.

  • For Offload Modeling: Go to Project Properties > Performance Modeling and enter the CLI action option --select=<string> in the Other parameters field. For example, --select=5,10,12.

  • Mark the loop(s) of interest using the CLI action option --select=<string> (recommended) or --mark-up-list=<string> when running a Characterization with Trip Counts and FLOP collection enabled, Dependencies, or Memory Access Patterns analysis. For example, with the --select option:

    advisor --collect=tripcounts --flop --project-dir=./advi_results --select=5,10,12 -- ./myApplication

    Then run a Characterization with Trip Counts and FLOP collections enabled, Dependencies, or Memory Access Patterns analysis.

NOTE:

There are different ways to select loops is in the CLI environment:

  • The advisor CLI action options --mark-up-list=<string> and --select=<string> merely simulate enabling a GUI checkbox when used within -collect action. They are active only for the duration of the --collect command.

  • The same options used with advisor CLI action --mark-up-loops actually enable a GUI checkbox. They are active beyond the duration of the -mark-up-loops command and applies to all downstream analyses, such as Characterization with Trip Counts and FLOP collection enabled, Dependencies, Memory Access Patterns.

Select Loops by Source File/Line Number

Minimize collection overhead.

Applicable analyses: Characterization with Trip Counts and FLOP collection enabled, Dependencies, Memory Access Patterns.

Use when...

  • You want to perform a deeper analysis on only a few loops.

  • CLI environment: You are analyzing a target application for which you have access to source code and can identify source file/line numbers.

Note: In the commands below, make sure to replace the myApplication with your application executable path and name before executing a command. If your application requires additional command line options, add them after the executable name.

Prerequisites:

  1. Run a Survey analysis.

  2. advisor CLI environment: If necessary, identify the source file and line number for the loops of interest.

    advisor --report=survey --project-dir=./advi_results -- ./myApplication

After performing the prerequisites, do one of the following:

  • For Vectorization and CPU Roofline: Mark the loop(s) of interest by enabling the associated checkbox on the Survey report.

    Then run a Characterization with Trip Counts and FLOP collection enabled, Dependencies, or Memory Access Patterns analysis.

  • For Offload Modeling: Go to Project Properties > Performance Modeling and enter the CLI action option --select=<string> in the Other parameters field. For example, --select=foo.cpp:34,bar.cpp:192.

  • Mark the loop(s) of interest using the CLI action option --select=<string> (recommended) or --mark-up-list=<string> for a Characterization with Trip C