tenfourfox/devtools/client/performance/docs/markers.md

Timeline Markers

Common

• DOMHighResTimeStamp start
• DOMHighResTimeStamp end
• DOMString name
• object? stack
• object? endStack
• unsigned short processType;
• boolean isOffMainThread;

The processType a GeckoProcessType enum listed in xpcom/build/nsXULAppAPI.h, specifying if this marker originates in a content, chrome, plugin etc. process. Additionally, markers may be created from any thread on those processes, and isOffMainThread highights whether or not they're from the main thread. The most common type of marker is probably going to be from a GeckoProcessType_Content's main thread when debugging content.

DOMEvent

Triggered when a DOM event occurs, like a click or a keypress.

• unsigned short eventPhase - a number indicating what phase this event is in (target, bubbling, capturing, maps to Ci.nsIDOMEvent constants)
• DOMString type - the type of event, like "keypress" or "click"

Reflow

Reflow markers (labeled as "Layout") indicate when a change has occurred to a DOM element's positioning that requires the frame tree (rendering representation of the DOM) to figure out the new position of a handful of elements. Fired via PresShell::DoReflow

Paint

• sequence<{ long height, long width, long x, long y }> rectangles - An array of rectangle objects indicating where painting has occurred.

Styles

Style markers (labeled as "Recalculating Styles") are triggered when Gecko needs to figure out the computational style of an element. Fired via RestyleTracker::DoProcessRestyles when there are elements to restyle.

• DOMString restyleHint - A string indicating what kind of restyling will need to be processed; for example "eRestyle_StyleAttribute" is relatively cheap, whereas "eRestyle_Subtree" is more expensive. The hint can be a string of any amount of the following, separated via " | ". All future restyleHints are from RestyleManager::RestyleHintToString.

  • "eRestyle_Self"
  • "eRestyle_Subtree"
  • "eRestyle_LaterSiblings"
  • "eRestyle_CSSTransitions"
  • "eRestyle_CSSAnimations"
  • "eRestyle_SVGAttrAnimations"
  • "eRestyle_StyleAttribute"
  • "eRestyle_StyleAttribute_Animations"
  • "eRestyle_Force"
  • "eRestyle_ForceDescendants"

Javascript

Javascript markers are emitted indicating when JS execution begins and ends, with a reason that triggered it (causeName), like a requestAnimationFrame or a setTimeout.

• string causeName - The reason that JS was entered. There are many possible reasons, and the interesting ones to show web developers (triggered by content) are:

  • "<script> element"
  • "EventListener.handleEvent"
  • "setInterval handler"
  • "setTimeout handler"
  • "FrameRequestCallback"
  • "EventHandlerNonNull"
  • "promise callback"
  • "promise initializer"
  • "Worker runnable"

  There are also many more potential JS causes, some which are just internally used and won't emit a marker, but the below ones are only of interest to Gecko hackers, most likely

  • "promise thenable"
  • "worker runnable"
  • "nsHTTPIndex set HTTPIndex property"
  • "XPCWrappedJS method call"
  • "nsHTTPIndex OnFTPControlLog"
  • "XPCWrappedJS QueryInterface"
  • "xpcshell argument processing”
  • "XPConnect sandbox evaluation "
  • "component loader report global"
  • "component loader load module"
  • "Cross-Process Object Wrapper call/construct"
  • "Cross-Process Object Wrapper ’set'"
  • "Cross-Process Object Wrapper 'get'"
  • "nsXULTemplateBuilder creation"
  • "TestShellCommand"
  • "precompiled XUL <script> element"
  • "XBL <field> initialization "
  • "NPAPI NPN_evaluate"
  • "NPAPI get"
  • "NPAPI set"
  • "NPAPI doInvoke"
  • "javascript: URI"
  • "geolocation.always_precise indexing"
  • "geolocation.app_settings enumeration"
  • "WebIDL dictionary creation"
  • "XBL <constructor>/<destructor> invocation"
  • "message manager script load"
  • "message handler script load"
  • "nsGlobalWindow report new global"

GarbageCollection

Emitted after a full GC cycle has completed (which is after any number of incremental slices).

• DOMString causeName - The reason for a GC event to occur. A full list of GC reasons can be found on MDN.
• DOMString nonincremenetalReason - If the GC could not do an incremental GC (smaller, quick GC events), and we have to walk the entire heap and GC everything marked, then the reason listed here is why.

nsCycleCollector::Collect

An nsCycleCollector::Collect marker is emitted for each incremental cycle collection slice and each non-incremental cycle collection.

nsCycleCollector::ForgetSkippable

nsCycleCollector::ForgetSkippable is presented as "Cycle Collection", but in reality it is preparation/pre-optimization for cycle collection, and not the actual tracing of edges and collecting of cycles.

ConsoleTime

A marker generated via console.time() and console.timeEnd().

• DOMString causeName - the label passed into console.time(label) and console.timeEnd(label) if passed in.

TimeStamp

A marker generated via console.timeStamp(label).

• DOMString causeName - the label passed into console.timeStamp(label) if passed in.

document::DOMContentLoaded

A marker generated when the DOMContentLoaded event is fired.

document::Load

A marker generated when the document's "load" event is fired.

Parse HTML

Parse XML

Worker

Emitted whenever there's an operation dealing with Workers (any kind of worker, Web Workers, Service Workers etc.). Currently there are 4 types of operations being tracked: serializing/deserializing data on the main thread, and also serializing/deserializing data off the main thread.

• ProfileTimelineWorkerOperationType operationType - the type of operation being done by the Worker or the main thread when dealing with workers. Can be one of the following enums defined in ProfileTimelineMarker.webidl
  • "serializeDataOffMainThread"
  • "serializeDataOnMainThread"
  • "deserializeDataOffMainThread"
  • "deserializeDataOnMainThread"

Composite

Composite markers trace the actual time an inner composite operation took on the compositor thread. Currently, these markers are only especially interesting for Gecko platform developers, and thus disabled by default.

CompositeForwardTransaction

Markers generated when the IPC request was made to the compositor from the child process's main thread.