Mach Try Perf

To make it easier for developers to find the tests they need to run we built a perf-specific try selector called ./mach try perf. With this tool, you no longer need to remember the obfuscated platform and test names that you need to target for your tests. Instead, the new interface shows test categories along with a simplified name of the platform that they will run on.

When you trigger a try run from the perf selector, two try runs will be created. One with your changes, and one without. In your console, after you trigger the try runs, you’ll find a PerfCompare link that will bring you directly to a comparison of the two pushes when they have completed.

The tool is built to be conservative about the number of tests to run, so if you are looking for something that is not listed, it’s likely hidden behind a flag found in the –help. Here’s a small sample of what you’ll find there which highlights the most relevant flags:

$ ./mach try perf --help

    perf arguments:
        --show-all            Show all available tasks.
        --android             Show android test categories (disabled by default).
        --chrome              Show tests available for Chrome-based browsers (disabled by default).
        --safari              Show tests available for Safari (disabled by default).
        --live-sites          Run tasks with live sites (if possible). You can also use the `live-sites` variant.
        --profile             Run tasks with profiling (if possible). You can also use the `profiling` variant.
        --single-run          Run tasks without a comparison
        --variants [ [ ...]]  Select variants to display in the selector from: no-fission, bytecode-cached, live-sites, profiling, swr
        --platforms [ [ ...]]
                            Select specific platforms to target. Android only available with --android. Available platforms: android-a51, android,
                            windows, linux, macosx, desktop
        --apps [ [ ...]]      Select specific applications to target from: firefox, chrome, chromium, geckoview, fenix, chrome-m, safari

    task configuration arguments:
        --artifact            Force artifact builds where possible.

Standard Usage

To use mach try perf simply call ./mach try perf. This will open an interface for test selection like so:

Mach try perf with default options

Select the categories you’d like to run, hit enter, and wait for the tool to finish the pushes. Note that it can take some time to do both pushes, and you might not see logging for some time.

Chrome and Android

Android and chrome tests are disabled by default as they are often unneeded and waste our limited resources. If you need either of these, you can add –chrome and/or –android to the command like so ./mach try perf –android –chrome:

Mach try perf with android, and chrome options


If you are looking for any variants (e.g. no-fission, bytecode-cached, live-sites), use the –variants options like so ./mach try perf –variants live-sites. This will select all possible categories that could have live-sites tests.

Mach try perf with variants

Note that it is expected that the offered categories have extra variants (such as bytecode-cached) as we are showing all possible combinations that can include live-sites.


To target a particular platform you can use –platforms to only show categories with the given platforms.


In the future, this section will be populated dynamically. If you are wondering what the categories you selected will run, you can use –no-push to print out a list of tasks that will run like so:

$ ./mach try perf --no-push

Artifact builds enabled, pass --no-artifact to disable
Gathering tasks for Benchmarks desktop category
Executing queries: 'browsertime 'benchmark, !android 'shippable !-32 !clang, !live, !profil, !chrom
estimates: Runs 66 tasks (54 selected, 12 dependencies)
estimates: Total task duration 8:45:58
estimates: In the top 62% of durations
estimates: Should take about 1:04:58 (Finished around 2022-11-22 15:08)
Commit message:
Perf selections=Benchmarks desktop (queries='browsertime 'benchmark&!android 'shippable !-32 !clang&!live&!profil&!chrom)
Pushed via `mach try perf`
Calculated try_task_config.json:
    "env": {
        "TRY_SELECTOR": "fuzzy"
    "tasks": [
    "use-artifact-builds": true,
    "version": 1

Adding a New Category

It’s very easy to add a new category if needed, and you can do so by modifying the PerfParser categories attribute here. The following is an example of a complex category that gives a good idea of what you have available:

"Resource Usage": {
    "query": {
        "talos": ["'talos 'xperf | 'tp5"],
        "raptor": ["'power 'osx"],
        "awsy": ["'awsy"],
    "suites": ["talos", "raptor", "awsy"],
    "platform-restrictions": ["desktop"],
    "variant-restrictions": {
        "raptor": [],
        "talos": [],
    "app-restrictions": {
        "raptor": ["firefox"],
        "talos": ["firefox"],
    "tasks": [],
The following fields are available:
  • query: Set the queries to use for each suite you need.

  • suites: The suites that are needed for this category.

  • tasks: A hard-coded list of tasks to select.

  • platform-restrictions: The platforms that it can run on.

  • app-restrictions: A list of apps that the category can run.

  • variant-restrictions: A list of variants available for each suite.

Note that setting the App/Variant-Restriction fields should be used to restrict the available apps and variants, not expand them as the suites, apps, and platforms combined already provide the largest coverage. The restrictions should be used when you know certain things definitely won’t work, or will never be implemented for this category of tests. For instance, our Resource Usage tests only work on Firefox even though they may exist in Raptor which can run tests with Chrome.

Frequently Asked Questions (FAQ)

If you have any questions which aren’t already answered below please reach out to us in the perftest matrix channel.

  • How can I tell what a category or a set of selections will run?

    At the moment, you need to run your command with an additional option to see what will be run: ./mach try perf –no-push. See the Categories section for more information about this. In the future, we plan on having an dynamically updated list for the tasks in the Categories section of this document.

  • What’s the difference between `Pageload desktop`, and `Pageload desktop firefox`?

    If you simply ran ./mach try perf with no additional options, then there is no difference. If you start adding additional browsers to the try run with commands like ./mach try perf –chrome, then Pageload desktop will select all tests available for ALL browsers available, and Pageload desktop firefox will only select Firefox tests. When –chrome is provided, you’ll also see a Pageload desktop chrome option.

  • Help! I can’t find a test in any of the categories. What should I do?

    Use the option –show-all. This will let you select tests from the ./mach try fuzzy –full interface directly instead of the categories. You will always be able to find your tests this way. Please be careful with your task selections though as it’s easy to run far too many tests in this way!

Future Work

The future work for this tool can be found in this bug. Feel free to file improvments, and bugs against it.