Intel® VTune™ Profiler User Guide

User Guide

Contents

Window: Summary - Memory Usage

Use the
Summary
 window as your starting point of the performance analysis with the
Intel® VTune™
Profiler
. To access this window, select the
Memory Usage
viewpoint and click the
Summary
 sub-tab in the result tab.
Depending on the analysis type, the
Summary
 window provides the following application-level statistics in the
Memory Usage
viewpoint:
You may click the
Copy to Clipboard
 button to copy the content of the selected summary section to the clipboard.

Analysis Metrics

The
Summary
 window displays a list of memory-related CPU metrics that help you estimate an overall memory usage during application execution. For a metric description, hover over the corresponding question mark icon to read the pop-up help:
Memory Bound metrics are measured either as Clockticks or as Pipeline Slots. Metrics measured in Clockticks are less precise compared to the metrics measured in Pipeline Slots since they may overlap and their sum at some level does not necessarily match the parent metric value. But such metrics are still useful for identifying the dominant performance bottleneck in the code.
Mouse over a flagged value with the performance issue and read the recommendation for further analysis. For example, a high Memory Bound value typically indicates that a significant fraction of the execution pipeline slots could be stalled due to a demand memory load and stores. For further details, you may switch to the
Bottom-up
 window and explore metric data per memory object.
A high DRAM Bandwidth Bound metric value indicates that your system spent much time heavily utilizing the DRAM bandwidth. The calculation of this metric relies on the accurate maximum system DRAM bandwidth measurement provided in the
System Bandwidth
 section below.

System Bandwidth

This section provides various system bandwidth-related properties detected by the product. Depending on the number of sockets on your system, the following types of system bandwidth are measured:
Max DRAM System Bandwidth
Maximum DRAM bandwidth measured for the whole system (across all packages) by running a micro-benchmark before the collection starts. If the system has already been actively loaded at the moment of collection start (for example, with the attach mode), the value may be less accurate.
Max DRAM Single-Package Bandwidth
Maximum DRAM bandwidth for single package measured by running a micro-benchmark before the collection starts. If the system has already been actively loaded at the moment of collection start (for example, with the attach mode), the value may be less accurate.
These values are used to define default High, Medium and Low bandwidth utilization thresholds for the
Bandwidth Utilization Histogram
 and to scale over-time bandwidth graphs in the
Bottom-up
 view. By default, for Memory Analysis results the system bandwidth is measured automatically. To enable this functionality for custom analysis results, make sure to select the
Evaluate max DRAM bandwidth
 option.

Bandwidth Utilization Histogram

This histogram shows how much time the system bandwidth was utilized by a certain value (Bandwidth Domain) and provides thresholds to categorize bandwidth utilization as High, Medium and Low. You can set the threshold by moving sliders at the bottom.
If you switch to the
Bottom-up
window and group the grid data by
../Bandwidth Utilization Type/..
, you can identify functions or memory objects with high bandwidth utilization in the specific bandwidth domain.
If you select the
Interconnect
 domain, you will be able to check whether the performance of your application is limited by the bandwidth of Interconnect links (inter-socket connections). Then, you may switch to the
Bottom-up
 window and identify code and memory objects with NUMA issues.
Single-Package
 domains are displayed for the systems with two or more CPU packages and the histogram for them shows the distribution of the elapsed time per maximum bandwidth utilization
among all packages
. Use this data to identify situations where your application utilizes bandwidth only on a subset of CPU packages. In this case, the whole system bandwidth utilization represented by domains like DRAM may be low whereas the performance is in fact limited by bandwidth utilization.
  • Interconnect bandwidth analysis is supported by the
    VTune
    Profiler
     for Intel microarchitecture code name Ivy Bridge EP and later.
  • To learn bandwidth capabilities, refer to your system specifications or run appropriate benchmarks to measure them; for example, Intel Memory Latency Checker can provide maximum achievable DRAM and Interconnect bandwidth.

Top Memory Objects by Latency (Linux* Targets Only)

If you enabled the
Analyze memory object
 configuration option for the Memory Access analysis, the
Summary
 window in the
Memory Usage
 viewpoint displays memory objects (variables, data structures, arrays) that introduced the highest latency to the execution of your application.
  • Memory objects identification is supported only for Linux targets and only for processors based on Intel microarchitecture code name Sandy Bridge and later.
  • Only metrics based on DLA-capable hardware events are applicable to the memory objects analysis. For example, the CPU Time metric is based on a non DLA-capable Clockticks event, so cannot be applied to memory objects. Examples of applicable metrics are Loads, Stores, LLC Miss Count, and Average Latency.
Clicking an object in the table opens the
Bottom-up
 window with the grid data grouped by
Memory Object/Function/Allocation Stack
. The selected hotspot object is highlighted.

Top Tasks

This section provides a list of tasks that took most of the time to execute, where
tasks
 are either code regions marked with Task API, or system tasks enabled to monitor Ftrace* events, Atrace* events, Intel Media SDK programs, OpenCL™ kernels, and so on.
Clicking a task type in the table opens the grid view (for example, Bottom-up or Event Count) grouped by the
Task Type
 granularity. See Task Analysis for more information.

Latency Histogram

This histogram shows a distribution of loads per latency (in cycles).

Collection and Platform Info

This section provides the following data:
Application Command Line
Path to the target application.
Operating System
Operating system used for the collection.
Computer Name
Name of the computer used for the collection.
Result Size
Size of the result collected by the
VTune
Profiler
.
Collection start time
Start time (in UTC format) of the external collection. Explore the
Timeline
 pane to track the performance statistics provided by the custom collector over time.
Collection stop time
Stop time (in UTC format) of the external collection. Explore the
Timeline
 pane to track the performance statistics provided by the custom collector over time.
Collector type
Type of the data collector used for the analysis. The following types are possible:
CPU Information
Name
Name of the processor used for the collection.
Frequency
Frequency of the processor used for the collection.
Logical CPU Count
Logical CPU count for the machine used for the collection.
Physical Core Count
Number of physical cores on the system.
User Name
User launching the data collection. This field is available if you enabled the per-user event-based sampling collection mode during the product installation.
GPU Information
Name
Name of the Graphics installed on the system.
Vendor
GPU vendor.
Driver
Version of the graphics driver installed on the system.
Stepping
Microprocessor version.
EU Count
Number of execution units (EUs) in the
Render and GPGPU
 engine. This data is Intel® HD Graphics and Intel® Iris® Graphics (further: Intel Graphics) specific.
Max EU Thread Count
Maximum number of threads per execution unit. This data is Intel Graphics specific.
Max Core Frequency
Maximum frequency of the Graphics processor. This data is Intel Graphics specific.
Graphics Performance Analysis
GPU metrics collection is enabled on the hardware level. This data is Intel Graphics specific.
Some systems disable collection of extended metrics such as L3 misses, memory accesses, sampler busyness, SLM accesses, and others in the BIOS. On some systems you can set a BIOS option to enable this collection. The presence or absence of the option and its name are BIOS vendor specific. Look for the
Intel® Graphics Performance Analyzers
 option (or similar) in your BIOS and set it to
Enabled
.

Product and Performance Information

1

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