Bandwidth analysis type uses event-based sampling collection and is targeted for the Intel® Xeon Phi™ coprocessor (code name: Knights Corner).
Bandwidth analysis type measures main components of bus transactions. Comparing the transaction rate with a generic threshold helps understand whether the code is saturating the bandwidth, which is a major performance limitation. To analyze this problem, you need to calibrate the collection runs: for example, compare the rate for the profiled code with the by-design bandwidth limited benchmark (like those from STREAM benchmarks).
To see the full list of events used for this analysis type:
Click the Image may be NSFW.
Clik here to view.
(standalone GUI)/Image may be NSFW.
Clik here to view. (Visual Studio IDE) New Analysis toolbar button.The Analysis Type window opens.
From the left pane, select Microarchitecture Analysis > Bandwidth.
The Bandwidth Analysis configuration pane opens on the right. The Details section provides a table with the processor events used for this analysis type.
Note
Analysis on the Intel Xeon Phi coprocessor is supported with the VTune Amplifier XE only. You can see a list of analysis types applicable to the coprocessor analysis only when you specify the Intel Xeon Phi coprocessor (native) or Intel Xeon Phi coprocessor (host launch)target system type in the Project Properties: Target tab.
You can choose to view Bandwidth analysis results in any of the following viewpoints:
Viewpoint | Description |
|---|---|
Hardware Event Counts | Displays the event count for all collected processor events. While the Hardware Event Sample Counts viewpoint provides the actual number of samples collected for an event, Hardware Event Count viewpoint estimates the number of times this event occurred during the collection. |
Hardware Event Sample Counts | Displays the sample count for all collected processor events. While the Hardware Event Counts viewpoint estimates the number of times an event occurred during the collection, the Hardware Event Sample Counts viewpoint provides the actual number of samples collected for this event. |
Hardware Issues | Helps identify where the application is not making the best use of available hardware resources. This viewpoint displays metrics derived from hardware performance counters. Hover over the highlighted metrics values in the grid to read why the extreme value might represent a performance problem. |
Hotspots | Helps identify hotspots - code regions in the application that consume a lot of CPU time. |
Task Time | Visualizes tasks, logical units of work on specific threads, based on ITT API annotations. Identify tasks with the highest execution time and analyze threads responsible for a particular task. |
These viewpoints may include the following windows:
Summary window displays statistics on the overall application execution.
Bottom-up pane displays performance data per metric (event ratio/event count/sample count) for each hotspot function.
Top-down Tree window displays hotspot functions in the call tree, performance metrics for a function only (Self value) and for a function and its children together (Total value).
PMU Events window displays count for PMU events selected for the analysis.
Uncore Events window displays count for uncore events selected for the analysis. If there are no uncore events, the upper pane of the window is empty.
Tasks, Tasks over Time, and Tasks by Threads windows provide details on tasks specified in your code with the Task API.