Traces UI

This WebUI implements chrome://traces which contains tools for performance investigation through tracing.

Scenarios

chrome://traces/scenarios gives control over the tracing scenario configurations. A Chrome tracing scenarios config allows automatic trace collection by defining a set of scenarios, each associated with specific tracing configs. Scenarios are enrolled based on a set of start and stop rules that delimitate a meaningful tracing interval, usually covering a user journey or a guardian metric (e.g. FirstContentfulPaint).

You can manually enroll in local "preset" scenarios through chrome://traces/scenarios UI.

Note If you are here because you'd like to collect a trace for a recurrent performance issue, consider enrolling in the "AlwaysOnScenario" scenario. Check the descriptions at chrome://traces/scenarios to learn more about available scenarios.

On pre-stable channels, you may already be enrolled in scenarios as part of field traces.

You can additionally select a custom scenarios config as a proto (.pb) or base64 encoded (.txt) file; this is meant for someone who wants to test a new config with custom triggers. If you are a googler, take a look at go/how-do-i-chrometto#how-do-i-test-background-tracing-setup-locally.

1. Create a new config.pbtxt file anywhere on your desktop. Copy the example config below and save the file.

scenarios: {
  scenario_name: "Test"
  trace_config: {
    data_sources: {
      config: {
        name: "track_event"
        track_event_config: {
          disabled_categories: ["*"],
          enabled_categories: ["toplevel"]
        },
      }
    }
    data_sources: { config: { name: "org.chromium.trace_metadata2" } }
  }
  start_rules: {
    name: "Timer Start"
    delay_ms: 0
  }
  upload_rules: {
    name: "Timer End"
    delay_ms: 5000
  }
}

2. Compile the proto with:

<outdir>/protoc --encode=perfetto.protos.ChromeFieldTracingConfig \
--proto_path=third_party/perfetto third_party/perfetto/protos/perfetto/config/\
chrome/scenario_config.proto < config.pbtxt > config.pb

config.pbtxt is the absolute path where your file is on your desktop. Keep the < > around config.pbtxt from the command above.

3. Select the resulting file in chrome://traces/scenarios, or run chrome with command line:

--enable-background-tracing=config.pb

Reports

When a tracing scenario triggers trace collection, the trace will appear in the reports list at chrome://traces. The .pb trace can be downloaded and opened with perfetto or shared with chromium developers. You can also upload the report and share the trace ID on a crbug.

Note Trace uploads requires enabling privacy filters at chrome://traces/scenarios

Recorder

chrome://traces/recorder provides a UI for manual trace collection, either

• Given a trace config as a base64 encoded, passed a ?trace_config= argument in URL.

Note If you're not sure what config you need, consider simply using the following URL:

chrome://traces/recorder?trace_config=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%3D%3D

• Use selectors UI to craft a custom trace config. The resulting config is synced to URL which can be shared.

Once you have a trace config, simply use "Start Tracing" and "Stop Tracing". Once the tracing session ends, a .pb trace is downloaded, which can be opened with perfetto or shared with chromium developers.

CHANGELOG

M141:

• Fix scroll in chrome://traces/scenarios
• chrome://traces/recorder adds UI for ETW data source.

M140:

• chrome://traces/recorder adds UI for most trace config.

M139:

• Basic support for chrome://traces/recorder given a trace config in URL
• Improved UI for chrome://traces/scenarios showing scenarios state.