Enabling No Overhead Profiling - 2022.1 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

Document ID
Release Date
2022.1 English
When profiling is enabled in xrt.ini with opencl_trace there is operational overhead added and events in the timeline can show longer delay in between events. However, XRT provides a no-overhead option to dump the OpenCL events on the timeline. It is a simple method of displaying events on the timeline without any overhead.
Tip: You cannot specify any host side profiling or this overrides the no-overhead approach. However, you can use this approach with device_trace, which profiles the device but does not add overhead to the host application.

Because the goal is to provide visibility into events with absolutely zero overhead, there are limitations to the number of events that can be logged. Additionally, there is no command queue information in this view, so this view is not intended as a replacement of the more detailed Timeline Trace.

You can use the "no overhead" view to confirm OpenCL command dependencies and to observe actual event overhead for the command execution from the host application.

Add the following switch in xrt.ini to enable OpenCL events. The beginning and end of event capturing can be controlled as shown below:
#xocl_event_begin= 0 (default)
#xocl_event_end=1000 (default)

By default only 1000 events can be visualized.

After the run, if no xrt.run_summary is generated, you can use the following steps to generate a .wdb file to view in Vitis Analyzer:
vp_analyze xocl -i xocl.log // generates debug_log.csv
vp_analyze trace -i debug_log.csv // generates debug_log.wdb
vitis_analyzer debug_log.wdb // loads the wdb file in Vitis analyzer
Figure 1. No Overhead Timeline
Table 1. Options for OpenCL Profiling
Trace Information Captured Profile Overhead Use Case xrt.ini Switches
Complete High For debug purposes like the early stage of application development. opencl_trace = true
Partial Low When profile overhead is High and unexpected delay is experienced. lop_trace = true
Minimum No Only to confirm the cause of delay between events. xocl_debug = true