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Telemetry: Add a Measurement

Are you sure you want to add a measurement?

Writing a good measurement is really hard. We already have a bunch of measurements in tools/perf/measurements for you to use. If you are looking to write a new benchmark, you probably just need to add or modify an existing story set and you might need to add new metrics to an existing measurement. Think twice before you write another measurement.

What is a measurement?

A measurement is a python class that obtains a set of Numbers about a Page. Measurements must work for all pages, not just one specific page.

For example, let’s say my users often go to a specific page, click a button, and scroll a div that shows up. I could measure any number of things:

How long it takes to go to that URL in a fresh tab until the div shows up

How smoothly I can scroll a div

How much time I spend in key WebKit systems: javascript, style, layout,
paint, compositing

How much the memory footprint varies as I scroll the div

How much time I spend decoding images and painting the page

These are all examples of measurements.

How about Timeline-Based Measurement?

Timeline-Based Measurement is a new and preferred way for computing Telemetry metrics from traces in a unified manner. The code is contained in tools/telemetry/telemetry/web_perf.

For details about this approach, see the following documents: Why choose TimelineBasedMeasurement over other measurements?

How does TimelineBasedMeasurement work?

I think I need to write a new measurement, now what?

Please email with details about what you are trying to measure. We can help you get started and ensure that there are not existing measurements that you could use.