Fuchsia tracing library and utilities require access to the trace_manager
's services in the environment, which is typically set up by the boot sequence.
Traces are captured using the fx traceutil
host utility. To record a trace simply run the following on your development host:
fx traceutil record
This will:
This is a great place to start an investigation. It is also a good when you are reporting a bug and are unsure what data is useful.
Some additional command line arguments to fx traceutil record
include:
-duration <time>
Sets the duration of the trace in seconds.
-target <hostname or ip address>
Specifies one which target to take a trace. Useful if you have multiple targets on the same network or network discovery is not working.
For a complete list of command line arguments run fx traceutil record --help
.
Under the hood traceutil
uses the trace
utility on the Fuchsia target to interact with the tracing manager. To record a trace run the following in a shell on your target:
trace record
This will save your trace in /data/trace.json by default. For more information on, run trace --help
at a Fuchsia shell.
The Fuchsia tracing system uses Chromium's Trace-Viewer. The easiest way to view a JSON trace is to embed it into an HTML file with Trace-Viewer. To convert one or more JSON files run:
fx traceutil convert FILE ...
The HTML files written are standalone and can be opened in the Chrome web browser.
Tracing specification file is a JSON file that can be passed to trace record
in order to configure parameters of tracing. For those parameters that can be passed both on the command line and set in the specification file, the command line value overrides the one from the file.
The file supports the following top level-parameters:
app
: string, url of the application to be runargs
: array of strings, startup arguments to be passed to the applicationcategories
: array of strings, tracing categories to be enabledduration
: integer, duration of tracing in secondsmeasure
: array of measurement specifications, see BenchmarkingBenchmarking docs moved to a separate doc.
The tracing configuration is a JSON file consisting of a list of known category names and descriptions.
{ "categories": { "category1": "description1", "category2": "description2" ] }, "providers": { "provider-label": "file:///provider-to-start-automatically" } }