Metrics

axemclion edited this page Nov 11, 2014 · 13 revisions

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

Please use browserPerf.docs.metric to programmatically get the list of all metrics with documentation. All metrics are also defined in JSON under the docs directory in the project.

Chrome Timeline Metrics

These metrics are obtained from the Chrome Developer Tools timeline. They are the same metrics you see in the timeline when a web page is profiled.

Chrome Developer Tools timeline view

Name Unit Description
CompositeLayers ms The time spent compositing rendering layers into a screen image
DecodeImage ms The time spent decoding images
EvaluateScript ms The time spent evaluating the page's scripts
EventDispatch ms The time spent executing event handlers
FireAnimationFrame ms The time spent handling scheduled animation frame events
FunctionCall ms The time spent executing calls to top-level Javascript functions
GCEvent ms The time spent doing garbage collection during script execution
Layout ms The time spent on (re)flow, or constructing the rendering tree from the DOM tree
Paint ms The time spent rasterizing the page into bitmaps
PaintSetup ms The time spent converting DOM elements into a display list of drawing commands to paint
ParseHTML ms The time spent executing the engine's HTML parsing algorithm
Program ms The total time for all actions to render the page
RecalculateStyles ms The time spent recalculating element styling, when a reflow occurs
TimerFire ms The time spent executing timer-triggered handlers
XHRReadyStateChange ms The time spent handling handling changes to the ready state of XMLHTTPRequest's

Chrome Tracing Metrics

Name Unit Description
Mean Frame Time ms Average time taken to render each frame

Request Animation Frame Metrics

Name Unit Description
droppedFrameCount count The number of frames produced by the GPU were over 16.6ms apart
numFramesSentToScreen count The number of frames the GPU sent to the screen
numAnimationFrames count Total number of times requestAnimationFrame was called

Runtime PerfMetrics

Name Unit Description
ExpensiveEventHandlers count The number of event handlers that took more than 16ms
ExpensivePaints count The number of paints that took more than 16ms
GCInsideAnimation count The number of times Garbage was called during the scroll
Layers count The number of layers used for rendering
NodePerLayout count The number of nodes that need to be updated during layout
PaintedArea sq.pixels The amount of space painted during paints

NavTimingMetrics

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

Each of these numbers in the metrics indicate the time elapsed after the previous event.

The order of the event flow is

Navigation Timing API

Name Unit Description
connectStart ms The time immediately before the user agent started establishing the connection to the server to retrieve the document
connectEnd ms The time immediately after the user agent finished establishing the connection to the server to retrieve the document
domComplete ms The time immediately before the user agent set the document's readiness to complete
domContentLoadedEventStart ms The time immediately before the user agent fired the DOMContentLoaded event
domContentLoadedEventEnd ms The time immediately after the document's DOMContentLoaded event completed
domInteractive ms The time immidiately before the user agent set the document's readiness to interactive
domLoading ms The time immidiately before the user agent set the document's readiness to loading
domainLookupStart ms The time immediately before the user agent started the domain name lookup for the document
domainLookupEnd ms The time immidiately after the user agent finishes the domain name lookup for the document
fetchStart ms The time immediately before the user agent checks caches for resources OR starts fetching resources
firstPaint ms The time immediately before the first paint occurred
loadEventStart ms The time immediately before the load event was fired for the document
loadEventEnd ms The time the load event for the document completed
requestStart ms The time immediately before the user agent started requesting the document from the server
responseStart ms The time immediately after the user agent received the first byte of the server's response to the document request
You can’t perform that action at this time.
You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session.
Press h to open a hovercard with more details.