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Using the Intercept Layer for OpenCL Applications with Intel(R) VTune(tm) Amplifier XE

The Intercept Layer for OpenCL Applications can be built with support for the Intel(R) VTune(tm) Instrumentation and Tracing Technology (ITT) APIs, which can add information about OpenCL-related calls to VTune timegraphs. This document describes how to build the Intercept Layer for OpenCL Applications with ITT support, and how to set controls and VTune to display OpenCL events captured by the Intercept Layer for OpenCL Applications.

Why Use the Intercept Layer for OpenCL Applications?

Recent versions of VTune supports tracing OpenCL programs natively, however you still may want to use CLIntercept's VTune integration:

  • The VTune OpenCL tracing works for Intel(R) Processor Graphics only, however the Intercept Layer for OpenCL Applications's OpenCL tracing works for all OpenCL devices, including non-Intel OpenCL devices.
  • The VTune OpenCL tracing works for a subset of OpenCL calls, however the Intercept Layer for OpenCL Applications's OpenCL tracing works for all OpenCL calls, including some non-API calls such as event callbacks.
  • The Intercept Layer for OpenCL Applications's OpenCL tracing is very lightweight.

Building the Intercept Layer for OpenCL Applications with ITT Support

To build the CLIntercept Intercept Layer for OpenCL Applications with ITT support, be sure the "ENABLE_ITT" box is checked when configuring CMake:

CMake GUI ITT

You'll also want to be sure that the VTUNE_INCLUDE_DIR and VTUNE_ITTNOTIFY_LIB variables are detected correctly. They may be setup automatically, but for systems with non-standard install paths they may need to be setup manually.

So long as this box is checked and the include and lib variables are setup correctly, the Intercept Layer for OpenCL Applications should build without errors or warnings and include ITT support.

Configuring the Intercept Layer for OpenCL Applications for VTune

The main control to configure the Intercept Layer for OpenCL Applications for VTune is ITTCallLogging. This adds API call entry and exit information to VTune timegraphs.

Configuring VTune for the Intercept Layer for OpenCL Applications

To configure VTune for the Intercept Layer for OpenCL Applications, checked the box for 'Analyze user tasks, events, and counters', since the Intercept Layer for OpenCL Applications's ITT call logging is considered a "user event".

You do not need to check the box for 'Trace OpenCL and Media SDK programs (Intel Graphics only)'. This enables the native VTune support for OpenCL tracing. If this box is checked you'll likely see some OpenCL calls twice on the timegraph, since both the Intercept Layer for OpenCL Applications and native VTune tracing will be enabled.

VTune Config

Example VTune Output with the Intercept Layer for OpenCL Applications

Here is example output with ITTCallLogging. Note that all API calls are logged, including an event callback on a separate thread:

VTune Output

Limitations and Restrictions

The biggest limitation at the moment is that you don't get any "device timing" information in VTune, you only get information about host API calls. This means that you won't see output like the picture below that you'd get with the native VTune tracing:

VTune Device Timing

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