Recording a Fuchsia trace
This document describes how to record a trace with Fuchsia's tracing system.
Prerequisites
Before you attempt to record a trace, make sure you have done the following:
- Registered your component as a trace provider. See Registering a trace provider.
- Added tracing in your code. See Adding tracing in your code.
- Included the
toolsto your Fuchsia build. Thecoreproduct and most other products includetoolsby default. If your build configuration does not includetoolsbundle by default, then you can manually add it withfx set:
fx set PRODUCT.BOARD --with-base '//bundles:tools'
Use the utilities
Traces are recorded with the trace utility on a Fuchsia target.
The ffx trace start command, which you can run from
your development host, calls the trace utility on your Fuchsia target.
You can record a trace from your Fuchsia target from your development host or directly from the Fuchsia target.
From a development host {#from-a-development-host}
To record a trace for a Fuchsia target from a development host, run the following command:
Note: You can also configure parameters of tracing with a tracing specification file.
ffx trace start does the following:
- Starts a trace on the Fuchsia target with the default options.
- Runs the tracing until the
Enterkey is pressed, or the duration is reached if provided. - Prints the trace results from the Fuchsia target device to an output file on your development host.
For a complete list of the ffx trace start options, run ffx trace start --help.
Once you have the trace output file, you can convert and analyze that trace file.
From a Fuchsia target {#from-a-fuchsia-target}
To record a trace directly from a Fuchsia target, run the following command in a shell on your target:
Note: You can also configure parameters of tracing with a tracing specification file.
trace record
This saves your trace in /data/trace.json on your Fuchsia target by default.
For more information on the trace utility, run trace --help at a Fuchsia shell.
Once you have the trace output file, you can convert and analyze that trace file.