Metrics

Metrics

The following metrics are measured. The tool is modular and other custom metrics can be added.

NavTimingMetrics

These are calculated from window.performance.timing API in NavTimingMetrics. For more information about each metric, please the W3C Specification

Name	Unit
fetchStart	ms
domainLookupStart	ms
domainLookupEnd	ms
connectStart	ms
connectEnd	ms
requestStart	ms
responseStart	ms
domLoading	ms
domInteractive	ms
domContentLoadedEventStart	ms
domContentLoadedEventEnd	ms
domComplete	ms
loadEventStart	ms
loadEventEnd	ms

Firefox

Metrics in firefox are calculated using requestAnimationFrame and mozAfterPaint

• dom_content_loaded_time
• dropped_percent
• load_time
• mean_frame_time
• first_paint

Internet Explorer

Metrics are calculated using requestAnimationFrame and window.navigation.timing.msFirstPaint

• dom_content_loaded_time
• dropped_percent
• load_time
• mean_frame_time
• first_paint

TODO: Use xPerf for calculating GPU timings

Chrome

Code ported from Chromium Telemetry Smoothness and Loading benchmarks. Data is collected from timeline (developer tools) events and about:tracing BenchmarkInstrumentation::ImplThreadRenderingStats and BenchmarkInstrumentation::MainThreadRenderingStats. Most sites use the metrics in bold for comparisons.

• average_commit_time
• average_num_layers_drawn
• average_num_missing_tiles
• CompositeLayers
• DecodeImage
• dom_content_loaded_time_ms
• dropped_percent
• EvaluateScript
• EventDispatch
• FireAnimationFrame
• first_paint
• FunctionCall
• GCEvent
• jank
• Layout
• load_time_ms
• mean_frame_time
• mostly_smooth
• Paint
• PaintSetup
• ParseHTML
• percent_impl_scrolled
• Program
• RecalculateStyles
• ResizeImage
• texture_upload_count
• TimerFire
• total_texture_upload_time