Intel® Advisor User Guide

User Guide

Contents

Model Threading Parallelism

The Suitability
analysis
 examines your running serial program to provide approximate estimated performance characteristics of your annotated parallel sites. This shows you both the performance gain from running your parallel program on multiple CPUs and the likely impact of parallel overhead.
To choose the best places to add parallelism, locate the parallel sites that contribute the most to the overall program's gain. Because of the overhead of parallel execution - such as starting threads - certain parallel sites and tasks may not contribute to the overall program's gain, or may slow down its performance. After you identify such parallel sites or tasks that do not improve performance, either modify or eliminate their annotations.

Use the Suitability Report Window

After you run the Suitability tool, view its data in the
Suitability Report
 window. This window contains multiple areas:
Location in Window
Description
Upper
Any annotation-related error the Suitability tool detects appears at the top of the
Suitability Report
 window. If you see such errors, the displayed Suitability data may not be reliable. To view the source location associated with an error, click the button. To fix the error, read the displayed error message, modify your source code to fix the problem, rebuild your target executable, and run Suitability tool analysis again.
Upper-left
The upper-left area shows the
Maximum Program Gain for All Sites
 in the program. Your overall goal of adding parallelism is to increase the
Maximum Program Gain for All Sites
 so the parallel program will execute as fast as possible. The measured serial execution runtime, predicted parallel runtime, and any measured are displayed below
Maximum Program Gain for All Sites
. Use the predicted Suitability gain values to help you make informed decisions about where to add parallelism.
Upper-right
Use the upper-right row of to model performance. Choose a hardware configuration and threading model (parallel framework) values from the drop-down lists. If you select a
Target System
 for
Intel® Xeon Phi™
 processors, an additional value for total
Coprocessor Threads
 appears.
Below this row is a grid of data that shows the estimated performance of each parallel site detected during program execution. The
Site Label
 shows the argument to the site annotation. Examine the predicted
Site Gain
 and
Impact to Program Gain
 (higher values are better) to estimate how much each site contributes to the
Maximum Program Gain for All Sites
 for all sites (described above). To expand the data under
Combined Site Metrics
 or
Site Instance Metrics
, click the icon to the right of that heading; to collapse data, click to the right of that heading.
To show or hide the side command toolbar, click the Show side command toolbar or Hide side command toolbar icon.
Middle-left
If you choose a
Target System
 of
CPU
, to view detailed characteristics of the selected site as well as its tasks and locks, click the
Site Details
 tab.
The
Scalability of Maximum Site Gain
 graph summarizes performance for the selected site. The number of CPU processors or total number of coprocessor threads appears on the horizontal X axis and the target's predicted performance gain appears on the Y axis. To change the default
CPU Count
 and the
Maximum CPU Count
, set the Options value.
Lower-left
Below the graph is a list of issues that might be preventing better
predicted
 performance gains as well as a summary of serial and predicted parallel time. To expand a line, click the down arrow to the right of the item's name. Most issues are related to the
Runtime Modeling
. Later, you can use other Analyzer tools like to measure
actual
 performance of your parallel program.
Lower-middle
Use the
Loop Iterations (Tasks) Modeling
 (or
Tasks Modeling
) to experiment with different loop structures, iteration counts, and instance durations that might improve the predicted parallel performance.
Click
Apply
 to view the impact on the predicted performance.
Lower-right
Use the
Runtime Modeling
 to learn which parallel overhead categories might have an impact on parallel overhead. If you agree to address a category later by using the chosen parallel framework's capabilities or by tuning the parallel code after you have implemented parallelism, check that category.
Bottom-right
If the chosen
Target System
 is
Intel Xeon Phi
 or
Offload to Intel Xeon Phi
, additional options appear below the
Runtime Modeling
 area. To expand this area, click the down arrow to the right of
Intel Xeon Phi Advanced Modeling
.
Lower, after clicking
Site Details
 tab
If you chose a
Target System
 of
CPU
, the
Site Details
 tab shows details about the selected parallel site, as well as details for each task and lock executed in that site.
When using an active result (not a read-only result), you can change the modeling parameters. Changing modeling parameters updates the displayed data, except for
Loop Iterations (Tasks) Modeling
 or
Tasks Modeling
 (click
Apply
). These modeling parameters help you understand the sensitivity of your annotation choices so you can choose the best places to add parallelism, but the displayed data summary is not an accurate estimate of final execution time on any specific parallel hardware (general processor characteristics are used).
Later, before you add parallel code, you must choose one parallel framework (threading model) for your application.
To view the source code associated with a site, locate the list of sites (upper-right area ) and either:
  • Double-click a row (or right-click and select
    View Source
     from the context menu) to display the
    Suitability Source
     window. Later, to return to the
    Suitability Report
     window, click
    Suitability Report
    .
  • Right-click a row and select
    Edit Source
     from the context menu to display the corresponding source file in a code editor. When using the
    Intel® Advisor
     GUI on Linux* OS, the editor defined by the
    Options > Editor dialog box
     appears with the file open at the corresponding location. When using the
    Intel® Advisor
     GUI on Windows* OS, the file type association (or
    Open With
     dialog box) determines the editor used. When using Microsoft Visual Studio*, the Visual Studio code editor appears with the file open at the corresponding location. Later, to return to the
    Suitability Report
     or
    Suitability Source
     window:
    1. Click the
      Result
       tab.
    2. Click either
      Suitability Report
       or
      Suitability Source
      .

Use the Suitability Source Window

Within the
Suitability Source
 window, you can:
  • Use the
    Call Stack
     pane to view different source locations in the call stack.
  • Double-click a line (or right-click and select
    Edit Source
    ) to open the corresponding source file in a code editor. When using the
    Intel® Advisor
     GUI on Linux* OS, the editor defined by the
    Options > Editor dialog box
     appears with the file open at the corresponding location. When using the
    Intel Advisor
     GUI on Windows* OS, the file type association (or
    Open With
     dialog box) determines the editor used. When using Microsoft Visual Studio*, the Visual Studio code editor appears with the file open at the corresponding location. Later, to return to the
    Result
     tab, click
    Result
    .
  • Return to the
    Suitability Report
     window by clicking
    Suitability Report
    .
The
Suitability Report
,
Suitability Source
, and other
Intel Advisor
 windows appear within the
Result
 tab. There is one
Result
 tab for each project.

Understand the Scalability Graph in the Suitability Report

One of two different graphs appear depending on the chosen
Target System
. For an explanation of the Scalability Graph, see Suitability Report Overview.

Tips on Understanding the Performance Data

In the
Suitability Report
 window, you start at the top, select a site, look at its details in the
Suitability Report
 window, and examine its source code. You repeat this process to investigate each annotated site. View this information, and if needed, modify the annotations by using your code editor.
Use the following guidelines to evaluate the feasibility of each site:
  • If the
    Site Gain
     values for the selected site shows an estimated performance gain of 1.0 or less, the overhead of parallel thread execution exceeds the potential performance gains. Modify or remove the annotations for the task(s) and its enclosing site. Repeat this for each parallel site.
  • If the
    Site Gain
     values for the selected site shows a performance gain greater than 1.0, look at the site's contribution to the
    Maximum Program Gain for All Sites
    , which applies to all parallel sites. For sites that do not contribute significantly to the
    Maximum Program Gain for All Sites
    , modify or remove the annotations for the task(s) and its enclosing site. For sites that only contribute slightly to the
    Maximum Program Gain for All Sites
    , examine more closely the annotations and the assumptions about fixing the various overhead costs of parallel thread execution. In some cases, you may be able to adjust the annotations to improve the performance gain or reduce the overhead. Repeat this for each parallel site.
  • When the
    Maximum Program Gain for All Sites
     for all sites and the
    Site Gain
     values for all the sites show a moderate or significant performance gain, proceed to the next workflow step that uses the Dependencies tool to check your remaining annotated sites for data sharing problems.

Product and Performance Information

1

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