Intel® VTune™ Profiler User Guide

User Guide

Contents

Minimize Collection Overhead

Explore configuration options provided by the
Intel® VTune™
Profiler
 that incur collection overhead and increase the result size.
If required, consider disabling or modifying these options either by editing the predefined analysis configuration or by creating a new custom analysis type:

Hotspots Sampling Mode

When you select the Hotspots analysis, you can choose between the User-Mode Sampling (higher overhead) and Hardware Event-Based Sampling (lower overhead). The
Overhead
 diagram on the right adjusts to your settings and shows how each of them impacts on the collection overhead:

Collect Context Switches

This option enables collection of thread context switches for hardware event-based sampling collection and is available in a custom hardware event-based sampling analysis configuration.
To disable/modify this option for custom analysis:
From GUI:
  1. In the
    Configure Analysis
     window >
    HOW
     pane, click the Browse button and select the
    Custom Analysis >
    your_custom_analysis
     type.
  2. In the custom analysis configuration, de-select the
    Collect context switches
     option.
From CLI:
Use the
-knob enable-stack-collection=false
 option. For example: 
vtune -collect-with runsa -knob enable-stack-collection=false -knob event-config=CPU_CLK_UNHALTED.REF_TSC:sa=1800000,CPU_CLK_UNHALTED /home/test/sample

Sampling Interval

This option configures the amount of wall-clock time the
VTune
Profiler
 waits before collecting each sample. The smaller the Sampling Interval, the larger the number of samples collected and written to the disk. The minimal value of the sampling interval depends on the system:
  • 10 milliseconds for systems with a single CPU
  • 15 milliseconds for systems with multi-core CPUs
To disable/modify the sampling interval value:
From GUI:
  1. In the
    Configure Analysis
     window >
    HOW
     pane, click the Browse button and select an analysis type, for example,
    Hotspots
     and use the
    Hardware Event-based Sampling
     mode.
  2. For the
    CPU sampling interval, ms
     option, specify a required value.
From CLI:
Use the
-knob sampling-interval=<
value
>
 option. For example: 
vtune -collect-with runss -knob sampling-interval=100 -knob cpu-samples-mode=stack -knob signals-mode=stack -knob waits-mode=stack -knob io-mode=stack /home/test/sample

Stack Size

This option is used to specify the size of a raw stack (in bytes) to process during hardware event-based sampling collection. Zero value means unlimited size. Possible values are numbers between 0 and 2147483647.
To disable/modify this option:
From GUI:
  1. In the
    Configure Analysis
     window >
    HOW
     pane, click the Browse button and select the
    Custom Analysis >
    your_custom_analysis
     type.
  2. In the custom configuration, decrease the
    Stack size, in bytes
     value.
From CLI:
Use the
-stack-size
option, for example: 
vtune -collect-with runsa -knob enable-stack-collection=true -knob stack-size=8192 -knob enable-call-counts=true -app-working-dir /home/samples/nqueens_fortran -- /home/samples/nqueens_fortran/nqueens_parallel

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.