Trace-based benchmarking

  • Updated: 2018 Sep 18

This document describes how to use trace-based benchmarking to measure and track performance of Fuchsia apps.


Trace-based benchmarks measure the performance of an application by running it under tracing and analyzing the collected traces to compute performance metrics.

For a typical service application (application to which clients connect over FIDL), the following components participate in a benchmarking run:

  • service binary - the service being benchmarked.
  • benchmark app - a client app that connects to the service and exercises the usage patterns we are interested in benchmarking.
  • benchmark spec - a JSON file specifying which trace events captured during a run of the benchmark app should be measured, and how.

The same framework can be also used to benchmark single binaries (without the client-server split).


Trace-based benchmarks are run using the trace binary. The spec file needs to be passed to the tool as follows:

trace record --spec-file=<path to the spec file>

Specification file

The specification file configures tracing parameters and specifies measurements. (see examples/benchmark if you'd like to see a full example straight away)

The file supports the following top level-parameters:

  • app: string, url of the application to be run
  • args: array of strings, startup arguments to be passed to the application
  • categories: array of strings, tracing categories to be enabled
  • duration: integer, maximum duration of tracing in seconds
  • measure: array of measurement specifications, see below

Given the specification file, the trace tool runs the app with the given args for at most duration seconds and gathers trace events from the selected categories. Then, the tool computes the measurements specified in the measure section on the recorded trace events.


  "app": "benchmark_example",
  "args": [],
  "categories": ["benchmark"],
  "measure": [

For any tracing parameters that can be passed both as arguments to trace record and set in the specification file, the command line value overrides the one from the file.

Measurement types

The trace tool supports the following types of measurements:

  • duration
  • time_between
  • argument_value

A duration measurement targets a single trace event and computes the duration of its occurrences. The target trace event can be recorded as a duration, an async, or a flow event.


      "type": "duration",
      "event_name": "example",
      "event_category": "benchmark"

A time_between measurement targets two trace events with the specified anchors (either the beginning or the end of the events) and computes the time between the consecutive occurrences of the two. The target events can be “duration”, “async”, “flow” or “instant” (in which case the anchor doesn't matter). Takes arguments: first_event_name, first_event_category, first_event_anchor, second_event_name, second_event_category, second_event_anchor.


      "type": "time_between",
      "first_event_name": "task_end",
      "first_event_category": "benchmark",
      "second_event_name": "task_start",
      "second_event_category": "benchmark"

In the example above the time_between measurement captures the time between the two instant events and measures the time between the end of one task and the beginning of another.

An argument_value measurement is used to record a value of an argument passed to the trace event. Takes as arguments a name and category of the event, name of the argument to be recorded and unit in which it is measured. The type of trace event doesn't matter, but the recorded argument must have uint64 type.


      "type": "argument_value",
      "event_name": "example",
      "event_category": "benchmark",
      "argument_name": "disk_space_used",
      "argument_unit": "Mb"


It is possible to specify an exact number of expected samples. In order to do so, an optional parameter "expected_sample_count" with a positive value must be specified for a given measurement. In that case, if the number of recorded samples does not match the one provided, an error will be logged and the measurement will produce no results (failing the benchmark).

You can also specify the "split_first" flag to separate the first sample from the rest. This is useful for recording the “cold run” samples (see the best practices section). This flag is passed to the exported file as well, in compliance with the results schema.

Full example

See examples/benchmark for a full example of a traced-based benchmark.

This example can be run with the following command:

trace record --spec-file=/pkgfs/packages/benchmark/0/data/benchmark_example.tspec

Best practices

Consider reusing benchmark binaries

The separation between specification files and benchmark binaries allows to define multiple benchmarks based on a single benchmark binary. Note that you can parametrize the benchmark binary by taking command line arguments which can be set to different values in each spec file.

Record “cold run” samples separately

For any duration measurement that happens more than once, chances are that the first time has different performance characteristics that the subsequent ones. You can set "split_first": true to report and track the first sample separately.


By default, the results are printed on the command line in a human-friendly format.


If you prefer a machine-friendly format, pass the path to the output file to trace record as --benchmark-results-file=<file>. See the results schema for the format of the resulting file.

Dashboard upload

Dashboard upload integration and infra support is WIP as of March, 2018. See the dashboard user guide and the instructions for automating benchmarks.