diff --git a/packages/react-dom/index.classic.fb.js b/packages/react-dom/index.classic.fb.js
index 1f451d70348b..e946df7b76db 100644
--- a/packages/react-dom/index.classic.fb.js
+++ b/packages/react-dom/index.classic.fb.js
@@ -7,7 +7,6 @@
  * @flow
  */
 
-import {addUserTimingListener} from 'shared/ReactFeatureFlags';
 import {isEnabled} from './src/events/ReactDOMEventListener';
 
 import {__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED} from './src/client/ReactDOM';
@@ -17,8 +16,6 @@ Object.assign((__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED: any), {
   ReactBrowserEventEmitter: {
     isEnabled,
   },
-  // Perf experiment
-  addUserTimingListener,
 });
 
 export {
diff --git a/packages/react-reconciler/src/ReactDebugFiberPerf.js b/packages/react-reconciler/src/ReactDebugFiberPerf.js
deleted file mode 100644
index 63dcf1af59a0..000000000000
--- a/packages/react-reconciler/src/ReactDebugFiberPerf.js
+++ /dev/null
@@ -1,506 +0,0 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- */
-
-import type {Fiber} from './ReactFiber';
-
-import {enableUserTimingAPI} from 'shared/ReactFeatureFlags';
-import getComponentName from 'shared/getComponentName';
-import {
-  HostRoot,
-  HostComponent,
-  HostText,
-  HostPortal,
-  Fragment,
-  ContextProvider,
-  ContextConsumer,
-  Mode,
-  SuspenseComponent,
-} from './ReactWorkTags';
-
-type MeasurementPhase =
-  | 'componentWillMount'
-  | 'componentWillUnmount'
-  | 'componentWillReceiveProps'
-  | 'shouldComponentUpdate'
-  | 'componentWillUpdate'
-  | 'componentDidUpdate'
-  | 'componentDidMount'
-  | 'getChildContext'
-  | 'getSnapshotBeforeUpdate';
-
-// Prefix measurements so that it's possible to filter them.
-// Longer prefixes are hard to read in DevTools.
-const reactEmoji = '\u269B';
-const warningEmoji = '\u26D4';
-const supportsUserTiming =
-  typeof performance !== 'undefined' &&
-  typeof performance.mark === 'function' &&
-  typeof performance.clearMarks === 'function' &&
-  typeof performance.measure === 'function' &&
-  typeof performance.clearMeasures === 'function';
-
-// Keep track of current fiber so that we know the path to unwind on pause.
-// TODO: this looks the same as nextUnitOfWork in scheduler. Can we unify them?
-let currentFiber: Fiber | null = null;
-// If we're in the middle of user code, which fiber and method is it?
-// Reusing `currentFiber` would be confusing for this because user code fiber
-// can change during commit phase too, but we don't need to unwind it (since
-// lifecycles in the commit phase don't resemble a tree).
-let currentPhase: MeasurementPhase | null = null;
-let currentPhaseFiber: Fiber | null = null;
-// Did lifecycle hook schedule an update? This is often a performance problem,
-// so we will keep track of it, and include it in the report.
-// Track commits caused by cascading updates.
-let isCommitting: boolean = false;
-let hasScheduledUpdateInCurrentCommit: boolean = false;
-let hasScheduledUpdateInCurrentPhase: boolean = false;
-let commitCountInCurrentWorkLoop: number = 0;
-let effectCountInCurrentCommit: number = 0;
-let isWaitingForCallback: boolean = false;
-// During commits, we only show a measurement once per method name
-// to avoid stretch the commit phase with measurement overhead.
-const labelsInCurrentCommit: Set<string> = new Set();
-
-const formatMarkName = (markName: string) => {
-  return `${reactEmoji} ${markName}`;
-};
-
-const formatLabel = (label: string, warning: string | null) => {
-  const prefix = warning ? `${warningEmoji} ` : `${reactEmoji} `;
-  const suffix = warning ? ` Warning: ${warning}` : '';
-  return `${prefix}${label}${suffix}`;
-};
-
-const beginMark = (markName: string) => {
-  performance.mark(formatMarkName(markName));
-};
-
-const clearMark = (markName: string) => {
-  performance.clearMarks(formatMarkName(markName));
-};
-
-const endMark = (label: string, markName: string, warning: string | null) => {
-  const formattedMarkName = formatMarkName(markName);
-  const formattedLabel = formatLabel(label, warning);
-  try {
-    performance.measure(formattedLabel, formattedMarkName);
-  } catch (err) {
-    // If previous mark was missing for some reason, this will throw.
-    // This could only happen if React crashed in an unexpected place earlier.
-    // Don't pile on with more errors.
-  }
-  // Clear marks immediately to avoid growing buffer.
-  performance.clearMarks(formattedMarkName);
-  performance.clearMeasures(formattedLabel);
-};
-
-const getFiberMarkName = (label: string, debugID: number) => {
-  return `${label} (#${debugID})`;
-};
-
-const getFiberLabel = (
-  componentName: string,
-  isMounted: boolean,
-  phase: MeasurementPhase | null,
-) => {
-  if (phase === null) {
-    // These are composite component total time measurements.
-    return `${componentName} [${isMounted ? 'update' : 'mount'}]`;
-  } else {
-    // Composite component methods.
-    return `${componentName}.${phase}`;
-  }
-};
-
-const beginFiberMark = (
-  fiber: Fiber,
-  phase: MeasurementPhase | null,
-): boolean => {
-  const componentName = getComponentName(fiber.type) || 'Unknown';
-  const debugID = ((fiber._debugID: any): number);
-  const isMounted = fiber.alternate !== null;
-  const label = getFiberLabel(componentName, isMounted, phase);
-
-  if (isCommitting && labelsInCurrentCommit.has(label)) {
-    // During the commit phase, we don't show duplicate labels because
-    // there is a fixed overhead for every measurement, and we don't
-    // want to stretch the commit phase beyond necessary.
-    return false;
-  }
-  labelsInCurrentCommit.add(label);
-
-  const markName = getFiberMarkName(label, debugID);
-  beginMark(markName);
-  return true;
-};
-
-const clearFiberMark = (fiber: Fiber, phase: MeasurementPhase | null) => {
-  const componentName = getComponentName(fiber.type) || 'Unknown';
-  const debugID = ((fiber._debugID: any): number);
-  const isMounted = fiber.alternate !== null;
-  const label = getFiberLabel(componentName, isMounted, phase);
-  const markName = getFiberMarkName(label, debugID);
-  clearMark(markName);
-};
-
-const endFiberMark = (
-  fiber: Fiber,
-  phase: MeasurementPhase | null,
-  warning: string | null,
-) => {
-  const componentName = getComponentName(fiber.type) || 'Unknown';
-  const debugID = ((fiber._debugID: any): number);
-  const isMounted = fiber.alternate !== null;
-  const label = getFiberLabel(componentName, isMounted, phase);
-  const markName = getFiberMarkName(label, debugID);
-  endMark(label, markName, warning);
-};
-
-const shouldIgnoreFiber = (fiber: Fiber): boolean => {
-  // Host components should be skipped in the timeline.
-  // We could check typeof fiber.type, but does this work with RN?
-  switch (fiber.tag) {
-    case HostRoot:
-    case HostComponent:
-    case HostText:
-    case HostPortal:
-    case Fragment:
-    case ContextProvider:
-    case ContextConsumer:
-    case Mode:
-      return true;
-    default:
-      return false;
-  }
-};
-
-const clearPendingPhaseMeasurement = () => {
-  if (currentPhase !== null && currentPhaseFiber !== null) {
-    clearFiberMark(currentPhaseFiber, currentPhase);
-  }
-  currentPhaseFiber = null;
-  currentPhase = null;
-  hasScheduledUpdateInCurrentPhase = false;
-};
-
-const pauseTimers = () => {
-  // Stops all currently active measurements so that they can be resumed
-  // if we continue in a later deferred loop from the same unit of work.
-  let fiber = currentFiber;
-  while (fiber) {
-    if (fiber._debugIsCurrentlyTiming) {
-      endFiberMark(fiber, null, null);
-    }
-    fiber = fiber.return;
-  }
-};
-
-const resumeTimersRecursively = (fiber: Fiber) => {
-  if (fiber.return !== null) {
-    resumeTimersRecursively(fiber.return);
-  }
-  if (fiber._debugIsCurrentlyTiming) {
-    beginFiberMark(fiber, null);
-  }
-};
-
-const resumeTimers = () => {
-  // Resumes all measurements that were active during the last deferred loop.
-  if (currentFiber !== null) {
-    resumeTimersRecursively(currentFiber);
-  }
-};
-
-export function recordEffect(): void {
-  if (enableUserTimingAPI) {
-    effectCountInCurrentCommit++;
-  }
-}
-
-export function recordScheduleUpdate(): void {
-  if (enableUserTimingAPI) {
-    if (isCommitting) {
-      hasScheduledUpdateInCurrentCommit = true;
-    }
-    if (
-      currentPhase !== null &&
-      currentPhase !== 'componentWillMount' &&
-      currentPhase !== 'componentWillReceiveProps'
-    ) {
-      hasScheduledUpdateInCurrentPhase = true;
-    }
-  }
-}
-
-export function startRequestCallbackTimer(): void {
-  if (enableUserTimingAPI) {
-    if (supportsUserTiming && !isWaitingForCallback) {
-      isWaitingForCallback = true;
-      beginMark('(Waiting for async callback...)');
-    }
-  }
-}
-
-export function stopRequestCallbackTimer(didExpire: boolean): void {
-  if (enableUserTimingAPI) {
-    if (supportsUserTiming) {
-      isWaitingForCallback = false;
-      const warning = didExpire
-        ? 'Update expired; will flush synchronously'
-        : null;
-      endMark(
-        '(Waiting for async callback...)',
-        '(Waiting for async callback...)',
-        warning,
-      );
-    }
-  }
-}
-
-export function startWorkTimer(fiber: Fiber): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming || shouldIgnoreFiber(fiber)) {
-      return;
-    }
-    // If we pause, this is the fiber to unwind from.
-    currentFiber = fiber;
-    if (!beginFiberMark(fiber, null)) {
-      return;
-    }
-    fiber._debugIsCurrentlyTiming = true;
-  }
-}
-
-export function cancelWorkTimer(fiber: Fiber): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming || shouldIgnoreFiber(fiber)) {
-      return;
-    }
-    // Remember we shouldn't complete measurement for this fiber.
-    // Otherwise flamechart will be deep even for small updates.
-    fiber._debugIsCurrentlyTiming = false;
-    clearFiberMark(fiber, null);
-  }
-}
-
-export function stopWorkTimer(fiber: Fiber): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming || shouldIgnoreFiber(fiber)) {
-      return;
-    }
-    // If we pause, its parent is the fiber to unwind from.
-    currentFiber = fiber.return;
-    if (!fiber._debugIsCurrentlyTiming) {
-      return;
-    }
-    fiber._debugIsCurrentlyTiming = false;
-    endFiberMark(fiber, null, null);
-  }
-}
-
-export function stopFailedWorkTimer(fiber: Fiber): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming || shouldIgnoreFiber(fiber)) {
-      return;
-    }
-    // If we pause, its parent is the fiber to unwind from.
-    currentFiber = fiber.return;
-    if (!fiber._debugIsCurrentlyTiming) {
-      return;
-    }
-    fiber._debugIsCurrentlyTiming = false;
-    const warning =
-      fiber.tag === SuspenseComponent
-        ? 'Rendering was suspended'
-        : 'An error was thrown inside this error boundary';
-    endFiberMark(fiber, null, warning);
-  }
-}
-
-export function startPhaseTimer(fiber: Fiber, phase: MeasurementPhase): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    clearPendingPhaseMeasurement();
-    if (!beginFiberMark(fiber, phase)) {
-      return;
-    }
-    currentPhaseFiber = fiber;
-    currentPhase = phase;
-  }
-}
-
-export function stopPhaseTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    if (currentPhase !== null && currentPhaseFiber !== null) {
-      const warning = hasScheduledUpdateInCurrentPhase
-        ? 'Scheduled a cascading update'
-        : null;
-      endFiberMark(currentPhaseFiber, currentPhase, warning);
-    }
-    currentPhase = null;
-    currentPhaseFiber = null;
-  }
-}
-
-export function startWorkLoopTimer(nextUnitOfWork: Fiber | null): void {
-  if (enableUserTimingAPI) {
-    currentFiber = nextUnitOfWork;
-    if (!supportsUserTiming) {
-      return;
-    }
-    commitCountInCurrentWorkLoop = 0;
-    // This is top level call.
-    // Any other measurements are performed within.
-    beginMark('(React Tree Reconciliation)');
-    // Resume any measurements that were in progress during the last loop.
-    resumeTimers();
-  }
-}
-
-export function stopWorkLoopTimer(
-  interruptedBy: Fiber | null,
-  didCompleteRoot: boolean,
-): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    let warning = null;
-    if (interruptedBy !== null) {
-      if (interruptedBy.tag === HostRoot) {
-        warning = 'A top-level update interrupted the previous render';
-      } else {
-        const componentName = getComponentName(interruptedBy.type) || 'Unknown';
-        warning = `An update to ${componentName} interrupted the previous render`;
-      }
-    } else if (commitCountInCurrentWorkLoop > 1) {
-      warning = 'There were cascading updates';
-    }
-    commitCountInCurrentWorkLoop = 0;
-    let label = didCompleteRoot
-      ? '(React Tree Reconciliation: Completed Root)'
-      : '(React Tree Reconciliation: Yielded)';
-    // Pause any measurements until the next loop.
-    pauseTimers();
-    endMark(label, '(React Tree Reconciliation)', warning);
-  }
-}
-
-export function startCommitTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    isCommitting = true;
-    hasScheduledUpdateInCurrentCommit = false;
-    labelsInCurrentCommit.clear();
-    beginMark('(Committing Changes)');
-  }
-}
-
-export function stopCommitTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-
-    let warning = null;
-    if (hasScheduledUpdateInCurrentCommit) {
-      warning = 'Lifecycle hook scheduled a cascading update';
-    } else if (commitCountInCurrentWorkLoop > 0) {
-      warning = 'Caused by a cascading update in earlier commit';
-    }
-    hasScheduledUpdateInCurrentCommit = false;
-    commitCountInCurrentWorkLoop++;
-    isCommitting = false;
-    labelsInCurrentCommit.clear();
-
-    endMark('(Committing Changes)', '(Committing Changes)', warning);
-  }
-}
-
-export function startCommitSnapshotEffectsTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    effectCountInCurrentCommit = 0;
-    beginMark('(Committing Snapshot Effects)');
-  }
-}
-
-export function stopCommitSnapshotEffectsTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    const count = effectCountInCurrentCommit;
-    effectCountInCurrentCommit = 0;
-    endMark(
-      `(Committing Snapshot Effects: ${count} Total)`,
-      '(Committing Snapshot Effects)',
-      null,
-    );
-  }
-}
-
-export function startCommitHostEffectsTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    effectCountInCurrentCommit = 0;
-    beginMark('(Committing Host Effects)');
-  }
-}
-
-export function stopCommitHostEffectsTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    const count = effectCountInCurrentCommit;
-    effectCountInCurrentCommit = 0;
-    endMark(
-      `(Committing Host Effects: ${count} Total)`,
-      '(Committing Host Effects)',
-      null,
-    );
-  }
-}
-
-export function startCommitLifeCyclesTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    effectCountInCurrentCommit = 0;
-    beginMark('(Calling Lifecycle Methods)');
-  }
-}
-
-export function stopCommitLifeCyclesTimer(): void {
-  if (enableUserTimingAPI) {
-    if (!supportsUserTiming) {
-      return;
-    }
-    const count = effectCountInCurrentCommit;
-    effectCountInCurrentCommit = 0;
-    endMark(
-      `(Calling Lifecycle Methods: ${count} Total)`,
-      '(Calling Lifecycle Methods)',
-      null,
-    );
-  }
-}
diff --git a/packages/react-reconciler/src/ReactFiber.js b/packages/react-reconciler/src/ReactFiber.js
index 4f0af6fe331e..f84d7796c99b 100644
--- a/packages/react-reconciler/src/ReactFiber.js
+++ b/packages/react-reconciler/src/ReactFiber.js
@@ -31,7 +31,6 @@ import invariant from 'shared/invariant';
 import {
   enableProfilerTimer,
   enableFundamentalAPI,
-  enableUserTimingAPI,
   enableScopeAPI,
   enableBlocksAPI,
   throwEarlyForMysteriousError,
@@ -324,14 +323,9 @@ function FiberNode(
     this.treeBaseDuration = 0;
   }
 
-  // This is normally DEV-only except www when it adds listeners.
-  // TODO: remove the User Timing integration in favor of Root Events.
-  if (enableUserTimingAPI) {
-    this._debugID = debugCounter++;
-    this._debugIsCurrentlyTiming = false;
-  }
-
   if (__DEV__) {
+    // This isn't directly used but is handy for debugging internals:
+    this._debugID = debugCounter++;
     this._debugSource = null;
     this._debugOwner = null;
     this._debugNeedsRemount = false;
@@ -419,9 +413,7 @@ export function createWorkInProgress(current: Fiber, pendingProps: any): Fiber {
 
     if (__DEV__) {
       // DEV-only fields
-      if (enableUserTimingAPI) {
-        workInProgress._debugID = current._debugID;
-      }
+      workInProgress._debugID = current._debugID;
       workInProgress._debugSource = current._debugSource;
       workInProgress._debugOwner = current._debugOwner;
       workInProgress._debugHookTypes = current._debugHookTypes;
@@ -968,10 +960,7 @@ export function assignFiberPropertiesInDEV(
     target.selfBaseDuration = source.selfBaseDuration;
     target.treeBaseDuration = source.treeBaseDuration;
   }
-  if (enableUserTimingAPI) {
-    target._debugID = source._debugID;
-    target._debugIsCurrentlyTiming = source._debugIsCurrentlyTiming;
-  }
+  target._debugID = source._debugID;
   target._debugSource = source._debugSource;
   target._debugOwner = source._debugOwner;
   target._debugNeedsRemount = source._debugNeedsRemount;
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 2ffd2fe79c09..2c6472c60fc1 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -79,7 +79,6 @@ import {
   getCurrentFiberOwnerNameInDevOrNull,
   setIsRendering,
 } from './ReactCurrentFiber';
-import {startWorkTimer, cancelWorkTimer} from './ReactDebugFiberPerf';
 import {
   resolveFunctionForHotReloading,
   resolveForwardRefForHotReloading,
@@ -1128,9 +1127,6 @@ function mountLazyComponent(
   }
 
   const props = workInProgress.pendingProps;
-  // We can't start a User Timing measurement with correct label yet.
-  // Cancel and resume right after we know the tag.
-  cancelWorkTimer(workInProgress);
   let lazyComponent: LazyComponentType<any, any> = elementType;
   let payload = lazyComponent._payload;
   let init = lazyComponent._init;
@@ -1138,7 +1134,6 @@ function mountLazyComponent(
   // Store the unwrapped component in the type.
   workInProgress.type = Component;
   const resolvedTag = (workInProgress.tag = resolveLazyComponentTag(Component));
-  startWorkTimer(workInProgress);
   const resolvedProps = resolveDefaultProps(Component, props);
   let child;
   switch (resolvedTag) {
@@ -2886,8 +2881,6 @@ function bailoutOnAlreadyFinishedWork(
   workInProgress: Fiber,
   renderExpirationTime: ExpirationTime,
 ): Fiber | null {
-  cancelWorkTimer(workInProgress);
-
   if (current !== null) {
     // Reuse previous dependencies
     workInProgress.dependencies = current.dependencies;
diff --git a/packages/react-reconciler/src/ReactFiberClassComponent.js b/packages/react-reconciler/src/ReactFiberClassComponent.js
index 83eff60f9285..7065a64c0c0b 100644
--- a/packages/react-reconciler/src/ReactFiberClassComponent.js
+++ b/packages/react-reconciler/src/ReactFiberClassComponent.js
@@ -26,7 +26,6 @@ import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
-import {startPhaseTimer, stopPhaseTimer} from './ReactDebugFiberPerf';
 import {resolveDefaultProps} from './ReactFiberLazyComponent';
 import {StrictMode} from './ReactTypeOfMode';
 
@@ -271,13 +270,11 @@ function checkShouldComponentUpdate(
         instance.shouldComponentUpdate(newProps, newState, nextContext);
       }
     }
-    startPhaseTimer(workInProgress, 'shouldComponentUpdate');
     const shouldUpdate = instance.shouldComponentUpdate(
       newProps,
       newState,
       nextContext,
     );
-    stopPhaseTimer();
 
     if (__DEV__) {
       if (shouldUpdate === undefined) {
@@ -705,7 +702,6 @@ function constructClassInstance(
 }
 
 function callComponentWillMount(workInProgress, instance) {
-  startPhaseTimer(workInProgress, 'componentWillMount');
   const oldState = instance.state;
 
   if (typeof instance.componentWillMount === 'function') {
@@ -715,8 +711,6 @@ function callComponentWillMount(workInProgress, instance) {
     instance.UNSAFE_componentWillMount();
   }
 
-  stopPhaseTimer();
-
   if (oldState !== instance.state) {
     if (__DEV__) {
       console.error(
@@ -737,14 +731,12 @@ function callComponentWillReceiveProps(
   nextContext,
 ) {
   const oldState = instance.state;
-  startPhaseTimer(workInProgress, 'componentWillReceiveProps');
   if (typeof instance.componentWillReceiveProps === 'function') {
     instance.componentWillReceiveProps(newProps, nextContext);
   }
   if (typeof instance.UNSAFE_componentWillReceiveProps === 'function') {
     instance.UNSAFE_componentWillReceiveProps(newProps, nextContext);
   }
-  stopPhaseTimer();
 
   if (instance.state !== oldState) {
     if (__DEV__) {
@@ -961,14 +953,12 @@ function resumeMountClassInstance(
       (typeof instance.UNSAFE_componentWillMount === 'function' ||
         typeof instance.componentWillMount === 'function')
     ) {
-      startPhaseTimer(workInProgress, 'componentWillMount');
       if (typeof instance.componentWillMount === 'function') {
         instance.componentWillMount();
       }
       if (typeof instance.UNSAFE_componentWillMount === 'function') {
         instance.UNSAFE_componentWillMount();
       }
-      stopPhaseTimer();
     }
     if (typeof instance.componentDidMount === 'function') {
       workInProgress.effectTag |= Update;
@@ -1113,14 +1103,12 @@ function updateClassInstance(
       (typeof instance.UNSAFE_componentWillUpdate === 'function' ||
         typeof instance.componentWillUpdate === 'function')
     ) {
-      startPhaseTimer(workInProgress, 'componentWillUpdate');
       if (typeof instance.componentWillUpdate === 'function') {
         instance.componentWillUpdate(newProps, newState, nextContext);
       }
       if (typeof instance.UNSAFE_componentWillUpdate === 'function') {
         instance.UNSAFE_componentWillUpdate(newProps, newState, nextContext);
       }
-      stopPhaseTimer();
     }
     if (typeof instance.componentDidUpdate === 'function') {
       workInProgress.effectTag |= Update;
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.js b/packages/react-reconciler/src/ReactFiberCommitWork.js
index 5af821dfc8fd..1e993acb65bb 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.js
@@ -74,7 +74,6 @@ import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 
 import {onCommitUnmount} from './ReactFiberDevToolsHook';
-import {startPhaseTimer, stopPhaseTimer} from './ReactDebugFiberPerf';
 import {getStackByFiberInDevAndProd} from './ReactCurrentFiber';
 import {logCapturedError} from './ReactFiberErrorLogger';
 import {resolveDefaultProps} from './ReactFiberLazyComponent';
@@ -182,7 +181,6 @@ export function logError(boundary: Fiber, errorInfo: CapturedValue<mixed>) {
 }
 
 const callComponentWillUnmountWithTimer = function(current, instance) {
-  startPhaseTimer(current, 'componentWillUnmount');
   instance.props = current.memoizedProps;
   instance.state = current.memoizedState;
   if (
@@ -199,7 +197,6 @@ const callComponentWillUnmountWithTimer = function(current, instance) {
   } else {
     instance.componentWillUnmount();
   }
-  stopPhaseTimer();
 };
 
 // Capture errors so they don't interrupt unmounting.
@@ -280,7 +277,6 @@ function commitBeforeMutationLifeCycles(
         if (current !== null) {
           const prevProps = current.memoizedProps;
           const prevState = current.memoizedState;
-          startPhaseTimer(finishedWork, 'getSnapshotBeforeUpdate');
           const instance = finishedWork.stateNode;
           // We could update instance props and state here,
           // but instead we rely on them being set during last render.
@@ -330,7 +326,6 @@ function commitBeforeMutationLifeCycles(
             }
           }
           instance.__reactInternalSnapshotBeforeUpdate = snapshot;
-          stopPhaseTimer();
         }
       }
       return;
@@ -580,7 +575,6 @@ function commitLifeCycles(
       const instance = finishedWork.stateNode;
       if (finishedWork.effectTag & Update) {
         if (current === null) {
-          startPhaseTimer(finishedWork, 'componentDidMount');
           // We could update instance props and state here,
           // but instead we rely on them being set during last render.
           // TODO: revisit this when we implement resuming.
@@ -625,14 +619,12 @@ function commitLifeCycles(
           } else {
             instance.componentDidMount();
           }
-          stopPhaseTimer();
         } else {
           const prevProps =
             finishedWork.elementType === finishedWork.type
               ? current.memoizedProps
               : resolveDefaultProps(finishedWork.type, current.memoizedProps);
           const prevState = current.memoizedState;
-          startPhaseTimer(finishedWork, 'componentDidUpdate');
           // We could update instance props and state here,
           // but instead we rely on them being set during last render.
           // TODO: revisit this when we implement resuming.
@@ -685,7 +677,6 @@ function commitLifeCycles(
               instance.__reactInternalSnapshotBeforeUpdate,
             );
           }
-          stopPhaseTimer();
         }
       }
       const updateQueue = finishedWork.updateQueue;
diff --git a/packages/react-reconciler/src/ReactFiberContext.js b/packages/react-reconciler/src/ReactFiberContext.js
index 33ba72aeec10..d2e0b40431de 100644
--- a/packages/react-reconciler/src/ReactFiberContext.js
+++ b/packages/react-reconciler/src/ReactFiberContext.js
@@ -17,7 +17,6 @@ import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import checkPropTypes from 'shared/checkPropTypes';
 
-import {startPhaseTimer, stopPhaseTimer} from './ReactDebugFiberPerf';
 import {createCursor, push, pop} from './ReactFiberStack';
 
 let warnedAboutMissingGetChildContext;
@@ -203,9 +202,7 @@ function processChildContext(
     }
 
     let childContext;
-    startPhaseTimer(fiber, 'getChildContext');
     childContext = instance.getChildContext();
-    stopPhaseTimer();
     for (let contextKey in childContext) {
       invariant(
         contextKey in childContextTypes,
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.js b/packages/react-reconciler/src/ReactFiberWorkLoop.js
index ec80c6c91c45..276795d2cee9 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.js
@@ -21,7 +21,6 @@ import {
   warnAboutDeprecatedLifecycles,
   deferPassiveEffectCleanupDuringUnmount,
   runAllPassiveEffectDestroysBeforeCreates,
-  enableUserTimingAPI,
   enableSuspenseServerRenderer,
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
   enableProfilerTimer,
@@ -167,23 +166,6 @@ import {
   setCurrentFiber as setCurrentDebugFiberInDEV,
   getStackByFiberInDevAndProd,
 } from './ReactCurrentFiber';
-import {
-  recordEffect,
-  recordScheduleUpdate,
-  startWorkTimer,
-  stopWorkTimer,
-  stopFailedWorkTimer,
-  startWorkLoopTimer,
-  stopWorkLoopTimer,
-  startCommitTimer,
-  stopCommitTimer,
-  startCommitSnapshotEffectsTimer,
-  stopCommitSnapshotEffectsTimer,
-  startCommitHostEffectsTimer,
-  stopCommitHostEffectsTimer,
-  startCommitLifeCyclesTimer,
-  stopCommitLifeCyclesTimer,
-} from './ReactDebugFiberPerf';
 import {
   invokeGuardedCallback,
   hasCaughtError,
@@ -275,8 +257,6 @@ let rootWithNestedUpdates: FiberRoot | null = null;
 const NESTED_PASSIVE_UPDATE_LIMIT = 50;
 let nestedPassiveUpdateCount: number = 0;
 
-let interruptedBy: Fiber | null = null;
-
 // Marks the need to reschedule pending interactions at these expiration times
 // during the commit phase. This enables them to be traced across components
 // that spawn new work during render. E.g. hidden boundaries, suspended SSR
@@ -397,9 +377,6 @@ export function scheduleUpdateOnFiber(
     return;
   }
 
-  checkForInterruption(fiber, expirationTime);
-  recordScheduleUpdate();
-
   // TODO: computeExpirationForFiber also reads the priority. Pass the
   // priority as an argument to that function and this one.
   const priorityLevel = getCurrentPriorityLevel();
@@ -1410,7 +1387,6 @@ function renderRootSync(root, expirationTime) {
   }
 
   const prevInteractions = pushInteractions(root);
-  startWorkLoopTimer(workInProgress);
   do {
     try {
       workLoopSync();
@@ -1436,8 +1412,6 @@ function renderRootSync(root, expirationTime) {
     );
   }
 
-  stopFinishedWorkLoopTimer();
-
   // Set this to null to indicate there's no in-progress render.
   workInProgressRoot = null;
 
@@ -1466,7 +1440,6 @@ function renderRootConcurrent(root, expirationTime) {
   }
 
   const prevInteractions = pushInteractions(root);
-  startWorkLoopTimer(workInProgress);
   do {
     try {
       workLoopConcurrent();
@@ -1486,12 +1459,9 @@ function renderRootConcurrent(root, expirationTime) {
   // Check if the tree has completed.
   if (workInProgress !== null) {
     // Still work remaining.
-    stopInterruptedWorkLoopTimer();
     return RootIncomplete;
   } else {
     // Completed the tree.
-    stopFinishedWorkLoopTimer();
-
     // Set this to null to indicate there's no in-progress render.
     workInProgressRoot = null;
 
@@ -1513,8 +1483,6 @@ function performUnitOfWork(unitOfWork: Fiber): Fiber | null {
   // nothing should rely on this, but relying on it here means that we don't
   // need an additional field on the work in progress.
   const current = unitOfWork.alternate;
-
-  startWorkTimer(unitOfWork);
   setCurrentDebugFiberInDEV(unitOfWork);
 
   let next;
@@ -1563,7 +1531,6 @@ function completeUnitOfWork(unitOfWork: Fiber): Fiber | null {
         // Update render duration assuming we didn't error.
         stopProfilerTimerIfRunningAndRecordDelta(workInProgress, false);
       }
-      stopWorkTimer(workInProgress);
       resetCurrentDebugFiberInDEV();
       resetChildExpirationTime(workInProgress);
 
@@ -1640,13 +1607,9 @@ function completeUnitOfWork(unitOfWork: Fiber): Fiber | null {
         // back here again.
         // Since we're restarting, remove anything that is not a host effect
         // from the effect tag.
-        // TODO: The name stopFailedWorkTimer is misleading because Suspense
-        // also captures and restarts.
-        stopFailedWorkTimer(workInProgress);
         next.effectTag &= HostEffectMask;
         return next;
       }
-      stopWorkTimer(workInProgress);
 
       if (returnFiber !== null) {
         // Mark the parent fiber as incomplete and clear its effect list.
@@ -1792,8 +1755,6 @@ function commitRootImpl(root, renderPriorityLevel) {
   root.callbackPriority = NoPriority;
   root.nextKnownPendingLevel = NoWork;
 
-  startCommitTimer();
-
   // Update the first and last pending times on this root. The new first
   // pending time is whatever is left on the root fiber.
   const remainingExpirationTimeBeforeCommit = getRemainingExpirationTime(
@@ -1849,7 +1810,6 @@ function commitRootImpl(root, renderPriorityLevel) {
     // The first phase a "before mutation" phase. We use this phase to read the
     // state of the host tree right before we mutate it. This is where
     // getSnapshotBeforeUpdate is called.
-    startCommitSnapshotEffectsTimer();
     prepareForCommit(root.containerInfo);
     nextEffect = firstEffect;
     do {
@@ -1871,7 +1831,6 @@ function commitRootImpl(root, renderPriorityLevel) {
         }
       }
     } while (nextEffect !== null);
-    stopCommitSnapshotEffectsTimer();
 
     if (enableProfilerTimer) {
       // Mark the current commit time to be shared by all Profilers in this
@@ -1880,7 +1839,6 @@ function commitRootImpl(root, renderPriorityLevel) {
     }
 
     // The next phase is the mutation phase, where we mutate the host tree.
-    startCommitHostEffectsTimer();
     nextEffect = firstEffect;
     do {
       if (__DEV__) {
@@ -1907,7 +1865,6 @@ function commitRootImpl(root, renderPriorityLevel) {
         }
       }
     } while (nextEffect !== null);
-    stopCommitHostEffectsTimer();
     resetAfterCommit(root.containerInfo);
 
     // The work-in-progress tree is now the current tree. This must come after
@@ -1919,7 +1876,6 @@ function commitRootImpl(root, renderPriorityLevel) {
     // The next phase is the layout phase, where we call effects that read
     // the host tree after it's been mutated. The idiomatic use case for this is
     // layout, but class component lifecycles also fire here for legacy reasons.
-    startCommitLifeCyclesTimer();
     nextEffect = firstEffect;
     do {
       if (__DEV__) {
@@ -1946,7 +1902,6 @@ function commitRootImpl(root, renderPriorityLevel) {
         }
       }
     } while (nextEffect !== null);
-    stopCommitLifeCyclesTimer();
 
     nextEffect = null;
 
@@ -1964,19 +1919,11 @@ function commitRootImpl(root, renderPriorityLevel) {
     // Measure these anyway so the flamegraph explicitly shows that there were
     // no effects.
     // TODO: Maybe there's a better way to report this.
-    startCommitSnapshotEffectsTimer();
-    stopCommitSnapshotEffectsTimer();
     if (enableProfilerTimer) {
       recordCommitTime();
     }
-    startCommitHostEffectsTimer();
-    stopCommitHostEffectsTimer();
-    startCommitLifeCyclesTimer();
-    stopCommitLifeCyclesTimer();
   }
 
-  stopCommitTimer();
-
   const rootDidHavePassiveEffects = rootDoesHavePassiveEffects;
 
   if (rootDoesHavePassiveEffects) {
@@ -2075,7 +2022,6 @@ function commitBeforeMutationEffects() {
     const effectTag = nextEffect.effectTag;
     if ((effectTag & Snapshot) !== NoEffect) {
       setCurrentDebugFiberInDEV(nextEffect);
-      recordEffect();
 
       const current = nextEffect.alternate;
       commitBeforeMutationEffectOnFiber(current, nextEffect);
@@ -2166,9 +2112,6 @@ function commitMutationEffects(root: FiberRoot, renderPriorityLevel) {
       }
     }
 
-    // TODO: Only record a mutation effect if primaryEffectTag is non-zero.
-    recordEffect();
-
     resetCurrentDebugFiberInDEV();
     nextEffect = nextEffect.nextEffect;
   }
@@ -2185,7 +2128,6 @@ function commitLayoutEffects(
     const effectTag = nextEffect.effectTag;
 
     if (effectTag & (Update | Callback)) {
-      recordEffect();
       const current = nextEffect.alternate;
       commitLayoutEffectOnFiber(
         root,
@@ -2196,7 +2138,6 @@ function commitLayoutEffects(
     }
 
     if (effectTag & Ref) {
-      recordEffect();
       commitAttachRef(nextEffect);
     }
 
@@ -2755,32 +2696,6 @@ function flushRenderPhaseStrictModeWarningsInDEV() {
   }
 }
 
-function stopFinishedWorkLoopTimer() {
-  const didCompleteRoot = true;
-  stopWorkLoopTimer(interruptedBy, didCompleteRoot);
-  interruptedBy = null;
-}
-
-function stopInterruptedWorkLoopTimer() {
-  // TODO: Track which fiber caused the interruption.
-  const didCompleteRoot = false;
-  stopWorkLoopTimer(interruptedBy, didCompleteRoot);
-  interruptedBy = null;
-}
-
-function checkForInterruption(
-  fiberThatReceivedUpdate: Fiber,
-  updateExpirationTime: ExpirationTime,
-) {
-  if (
-    enableUserTimingAPI &&
-    workInProgressRoot !== null &&
-    updateExpirationTime > renderExpirationTime
-  ) {
-    interruptedBy = fiberThatReceivedUpdate;
-  }
-}
-
 let didWarnStateUpdateForUnmountedComponent: Set<string> | null = null;
 function warnAboutUpdateOnUnmountedFiberInDEV(fiber) {
   if (__DEV__) {
diff --git a/packages/react-reconciler/src/__tests__/ReactIncrementalPerf-test.internal.js b/packages/react-reconciler/src/__tests__/ReactIncrementalPerf-test.internal.js
deleted file mode 100644
index 08c569c23950..000000000000
--- a/packages/react-reconciler/src/__tests__/ReactIncrementalPerf-test.internal.js
+++ /dev/null
@@ -1,683 +0,0 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @emails react-core
- * @jest-environment node
- */
-
-'use strict';
-
-describe('ReactDebugFiberPerf', () => {
-  let React;
-  let ReactNoop;
-  let Scheduler;
-  let PropTypes;
-
-  let root;
-  let activeMeasure;
-  let knownMarks;
-  let knownMeasures;
-  let comments;
-
-  function resetFlamechart() {
-    root = {
-      children: [],
-      indent: -1,
-      markName: null,
-      label: null,
-      parent: null,
-      toString() {
-        return this.children.map(c => c.toString()).join('\n');
-      },
-    };
-    activeMeasure = root;
-    knownMarks = new Set();
-    knownMeasures = new Set();
-    comments = [];
-  }
-
-  function addComment(comment) {
-    comments.push(comment);
-  }
-
-  function getFlameChart() {
-    // Make sure we unwind the measurement stack every time.
-    expect(activeMeasure.indent).toBe(-1);
-    expect(activeMeasure).toBe(root);
-    // We should always clean them up because browsers
-    // buffer user timing measurements forever.
-    expect(knownMarks.size).toBe(0);
-    expect(knownMeasures.size).toBe(0);
-    return root.toString();
-  }
-
-  function createUserTimingPolyfill() {
-    // This is not a true polyfill, but it gives us enough
-    // to capture measurements in a readable tree-like output.
-    // Reference: https://developer.mozilla.org/en-US/docs/Web/API/User_Timing_API
-    return {
-      mark(markName) {
-        const measure = {
-          children: [],
-          indent: activeMeasure.indent + 1,
-          markName: markName,
-          // Will be assigned on measure() call:
-          label: null,
-          parent: activeMeasure,
-          comments,
-          toString() {
-            return (
-              [
-                ...this.comments.map(c => '  '.repeat(this.indent) + '// ' + c),
-                '  '.repeat(this.indent) + this.label,
-                ...this.children.map(c => c.toString()),
-              ].join('\n') +
-              // Extra newline after each root reconciliation
-              (this.indent === 0 ? '\n' : '')
-            );
-          },
-        };
-        comments = [];
-        // Step one level deeper
-        activeMeasure.children.push(measure);
-        activeMeasure = measure;
-        knownMarks.add(markName);
-      },
-      // We don't use the overload with three arguments.
-      measure(label, markName) {
-        if (markName !== activeMeasure.markName) {
-          // Fail the test.
-          console.error(
-            'Unexpected measure() call: "%s". Active mark is "%s".',
-            markName,
-            activeMeasure.markName,
-          );
-          // This exception will be caught and ignored
-          // because in the real implementation, we don't want
-          // to spam the console due to a React bug.
-          throw new Error('Unexpected measure() call.');
-        }
-        // Step one level up
-        activeMeasure.label = label;
-        activeMeasure = activeMeasure.parent;
-        knownMeasures.add(label);
-      },
-      clearMarks(markName) {
-        if (markName === activeMeasure.markName) {
-          // Step one level up if we're in this measure
-          activeMeasure = activeMeasure.parent;
-          activeMeasure.children.length--;
-        }
-        knownMarks.delete(markName);
-      },
-      clearMeasures(label) {
-        knownMeasures.delete(label);
-      },
-    };
-  }
-
-  function Parent(props) {
-    return <div>{props.children}</div>;
-  }
-
-  function Child(props) {
-    return <div>{props.children}</div>;
-  }
-
-  beforeEach(() => {
-    jest.resetModules();
-    resetFlamechart();
-    global.performance = createUserTimingPolyfill();
-
-    require('shared/ReactFeatureFlags').enableUserTimingAPI = true;
-    require('shared/ReactFeatureFlags').enableProfilerTimer = false;
-    require('shared/ReactFeatureFlags').replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
-    require('shared/ReactFeatureFlags').debugRenderPhaseSideEffectsForStrictMode = false;
-    require('scheduler/src/SchedulerFeatureFlags').enableProfiling = false;
-
-    // Import after the polyfill is set up:
-    React = require('react');
-    ReactNoop = require('react-noop-renderer');
-    Scheduler = require('scheduler');
-    PropTypes = require('prop-types');
-  });
-
-  afterEach(() => {
-    delete global.performance;
-  });
-
-  it('measures a simple reconciliation', () => {
-    ReactNoop.render(
-      <Parent>
-        <Child />
-      </Parent>,
-    );
-    addComment('Mount');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    ReactNoop.render(
-      <Parent>
-        <Child />
-      </Parent>,
-    );
-    addComment('Update');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    ReactNoop.render(null);
-    addComment('Unmount');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('properly displays the forwardRef component in measurements', () => {
-    const AnonymousForwardRef = React.forwardRef((props, ref) => (
-      <Child {...props} ref={ref} />
-    ));
-    const NamedForwardRef = React.forwardRef(function refForwarder(props, ref) {
-      return <Child {...props} ref={ref} />;
-    });
-    function notImportant(props, ref) {
-      return <Child {...props} ref={ref} />;
-    }
-    notImportant.displayName = 'OverriddenName';
-    const DisplayNamedForwardRef = React.forwardRef(notImportant);
-
-    ReactNoop.render(
-      <Parent>
-        <AnonymousForwardRef />
-        <NamedForwardRef />
-        <DisplayNamedForwardRef />
-      </Parent>,
-    );
-    addComment('Mount');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('does not include StrictMode or Profiler components in measurements', () => {
-    ReactNoop.render(
-      <React.Profiler id="test" onRender={jest.fn()}>
-        <React.StrictMode>
-          <Parent>
-            <Child />
-          </Parent>
-        </React.StrictMode>
-      </React.Profiler>,
-    );
-    addComment('Mount');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('does not include context provider or consumer in measurements', () => {
-    const {Consumer, Provider} = React.createContext(true);
-
-    ReactNoop.render(
-      <Provider value={false}>
-        <Parent>
-          <Consumer>{value => <Child value={value} />}</Consumer>
-        </Parent>
-      </Provider>,
-    );
-    addComment('Mount');
-    expect(Scheduler).toFlushWithoutYielding();
-
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('skips parents during setState', () => {
-    class A extends React.Component {
-      render() {
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    class B extends React.Component {
-      render() {
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    let a;
-    let b;
-    ReactNoop.render(
-      <Parent>
-        <Parent>
-          <Parent>
-            <A ref={inst => (a = inst)} />
-          </Parent>
-        </Parent>
-        <Parent>
-          <B ref={inst => (b = inst)} />
-        </Parent>
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    resetFlamechart();
-
-    a.setState({});
-    b.setState({});
-    addComment('Should include just A and B, no Parents');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('warns on cascading renders from setState', () => {
-    class Cascading extends React.Component {
-      componentDidMount() {
-        this.setState({});
-      }
-      render() {
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <Cascading />
-      </Parent>,
-    );
-    addComment('Should print a warning');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('warns on cascading renders from top-level render', () => {
-    class Cascading extends React.Component {
-      componentDidMount() {
-        ReactNoop.renderToRootWithID(<Child />, 'b');
-        addComment('Scheduling another root from componentDidMount');
-      }
-      render() {
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    ReactNoop.renderToRootWithID(<Cascading />, 'a');
-    addComment('Rendering the first root');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('does not treat setState from cWM or cWRP as cascading', () => {
-    class NotCascading extends React.Component {
-      UNSAFE_componentWillMount() {
-        this.setState({});
-      }
-      UNSAFE_componentWillReceiveProps() {
-        this.setState({});
-      }
-      render() {
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <NotCascading />
-      </Parent>,
-    );
-    addComment('Should not print a warning');
-    expect(() => expect(Scheduler).toFlushWithoutYielding()).toErrorDev(
-      [
-        'Using UNSAFE_componentWillMount in strict mode is not recommended',
-        'Using UNSAFE_componentWillReceiveProps in strict mode is not recommended',
-      ],
-      {withoutStack: true},
-    );
-    ReactNoop.render(
-      <Parent>
-        <NotCascading />
-      </Parent>,
-    );
-    addComment('Should not print a warning');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('captures all lifecycles', () => {
-    class AllLifecycles extends React.Component {
-      static childContextTypes = {
-        foo: PropTypes.any,
-      };
-      shouldComponentUpdate() {
-        return true;
-      }
-      getChildContext() {
-        return {foo: 42};
-      }
-      UNSAFE_componentWillMount() {}
-      componentDidMount() {}
-      UNSAFE_componentWillReceiveProps() {}
-      UNSAFE_componentWillUpdate() {}
-      componentDidUpdate() {}
-      componentWillUnmount() {}
-      render() {
-        return <div />;
-      }
-    }
-    ReactNoop.render(<AllLifecycles />);
-    addComment('Mount');
-    expect(() => expect(Scheduler).toFlushWithoutYielding()).toErrorDev(
-      [
-        'Using UNSAFE_componentWillMount in strict mode is not recommended',
-        'Using UNSAFE_componentWillReceiveProps in strict mode is not recommended',
-        'Using UNSAFE_componentWillUpdate in strict mode is not recommended',
-        'Legacy context API has been detected within a strict-mode tree',
-      ],
-      {withoutStack: 3},
-    );
-    ReactNoop.render(<AllLifecycles />);
-    addComment('Update');
-    expect(Scheduler).toFlushWithoutYielding();
-    ReactNoop.render(null);
-    addComment('Unmount');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('measures deprioritized work', () => {
-    addComment('Flush the parent');
-    ReactNoop.flushSync(() => {
-      ReactNoop.render(
-        <Parent>
-          <div hidden={true}>
-            <Child />
-          </div>
-        </Parent>,
-      );
-    });
-    addComment('Flush the child');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('measures deferred work in chunks', () => {
-    class A extends React.Component {
-      render() {
-        Scheduler.unstable_yieldValue('A');
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    class B extends React.Component {
-      render() {
-        Scheduler.unstable_yieldValue('B');
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    class C extends React.Component {
-      render() {
-        Scheduler.unstable_yieldValue('C');
-        return <div>{this.props.children}</div>;
-      }
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <A>
-          <Child />
-        </A>
-        <B>
-          <Child />
-        </B>
-        <C>
-          <Child />
-        </C>
-      </Parent>,
-    );
-    addComment('Start rendering through B');
-    expect(Scheduler).toFlushAndYieldThrough(['A', 'B']);
-    addComment('Complete the rest');
-    expect(Scheduler).toFlushAndYield(['C']);
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('recovers from fatal errors', () => {
-    function Baddie() {
-      throw new Error('Game over');
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <Baddie />
-      </Parent>,
-    );
-    try {
-      addComment('Will fatal');
-      expect(Scheduler).toFlushWithoutYielding();
-    } catch (err) {
-      expect(err.message).toBe('Game over');
-    }
-    ReactNoop.render(
-      <Parent>
-        <Child />
-      </Parent>,
-    );
-    addComment('Will reconcile from a clean state');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('recovers from caught errors', () => {
-    function Baddie() {
-      throw new Error('Game over');
-    }
-
-    function ErrorReport() {
-      return <div />;
-    }
-
-    class Boundary extends React.Component {
-      state = {error: null};
-      componentDidCatch(error) {
-        this.setState({error});
-      }
-      render() {
-        if (this.state.error) {
-          return <ErrorReport />;
-        }
-        return this.props.children;
-      }
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <Boundary>
-          <Parent>
-            <Baddie />
-          </Parent>
-        </Boundary>
-      </Parent>,
-    );
-    addComment('Stop on Baddie and restart from Boundary');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('deduplicates lifecycle names during commit to reduce overhead', () => {
-    class A extends React.Component {
-      componentDidUpdate() {}
-      render() {
-        return <div />;
-      }
-    }
-
-    class B extends React.Component {
-      componentDidUpdate(prevProps) {
-        if (this.props.cascade && !prevProps.cascade) {
-          this.setState({});
-        }
-      }
-      render() {
-        return <div />;
-      }
-    }
-
-    ReactNoop.render(
-      <Parent>
-        <A />
-        <B />
-        <A />
-        <B />
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    resetFlamechart();
-
-    ReactNoop.render(
-      <Parent>
-        <A />
-        <B />
-        <A />
-        <B />
-      </Parent>,
-    );
-    addComment('The commit phase should mention A and B just once');
-    expect(Scheduler).toFlushWithoutYielding();
-    ReactNoop.render(
-      <Parent>
-        <A />
-        <B />
-        <A />
-        <B cascade={true} />
-      </Parent>,
-    );
-    addComment("Because of deduplication, we don't know B was cascading,");
-    addComment('but we should still see the warning for the commit phase.');
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('supports portals', () => {
-    const portalContainer = ReactNoop.getOrCreateRootContainer(
-      'portalContainer',
-    );
-    ReactNoop.render(
-      <Parent>
-        {ReactNoop.createPortal(<Child />, portalContainer, null)}
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('supports memo', () => {
-    const MemoFoo = React.memo(function Foo() {
-      return <div />;
-    });
-    ReactNoop.render(
-      <Parent>
-        <MemoFoo />
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('supports Suspense and lazy', async () => {
-    function Spinner() {
-      return <span />;
-    }
-
-    function fakeImport(result) {
-      return {default: result};
-    }
-
-    let resolve;
-    const LazyFoo = React.lazy(
-      () =>
-        new Promise(r => {
-          resolve = r;
-        }),
-    );
-
-    // Initial render
-    ReactNoop.render(
-      <Parent>
-        <React.Suspense fallback={<Spinner />} />
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-
-    // Update that suspends
-    ReactNoop.render(
-      <Parent>
-        <React.Suspense fallback={<Spinner />}>
-          <LazyFoo />
-        </React.Suspense>
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-
-    resolve(
-      fakeImport(function Foo() {
-        return <div />;
-      }),
-    );
-
-    await Promise.resolve();
-
-    ReactNoop.render(
-      <Parent>
-        <React.Suspense>
-          <LazyFoo />
-        </React.Suspense>
-      </Parent>,
-    );
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('does not schedule an extra callback if setState is called during a synchronous commit phase', () => {
-    class Component extends React.Component {
-      state = {step: 1};
-      componentDidMount() {
-        this.setState({step: 2});
-      }
-      render() {
-        return <span prop={this.state.step} />;
-      }
-    }
-    ReactNoop.flushSync(() => {
-      ReactNoop.render(<Component />);
-    });
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('warns if an in-progress update is interrupted', () => {
-    function Foo() {
-      Scheduler.unstable_yieldValue('Foo');
-      return <span />;
-    }
-
-    ReactNoop.render(<Foo />);
-    ReactNoop.flushNextYield();
-    ReactNoop.flushSync(() => {
-      ReactNoop.render(<Foo />);
-    });
-    expect(Scheduler).toHaveYielded(['Foo']);
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-
-  it('warns if async work expires (starvation)', () => {
-    function Foo() {
-      return <span />;
-    }
-
-    ReactNoop.render(<Foo />);
-    ReactNoop.expire(6000);
-    expect(Scheduler).toFlushWithoutYielding();
-    expect(getFlameChart()).toMatchSnapshot();
-  });
-});
diff --git a/packages/react-reconciler/src/__tests__/__snapshots__/ReactIncrementalPerf-test.internal.js.snap b/packages/react-reconciler/src/__tests__/__snapshots__/ReactIncrementalPerf-test.internal.js.snap
deleted file mode 100644
index b438a6f7e678..000000000000
--- a/packages/react-reconciler/src/__tests__/__snapshots__/ReactIncrementalPerf-test.internal.js.snap
+++ /dev/null
@@ -1,477 +0,0 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
-
-exports[`ReactDebugFiberPerf captures all lifecycles 1`] = `
-"// Mount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ AllLifecycles [mount]
-    ⚛ AllLifecycles.componentWillMount
-    ⚛ AllLifecycles.getChildContext
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-    ⚛ AllLifecycles.componentDidMount
-
-// Update
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ AllLifecycles [update]
-    ⚛ AllLifecycles.componentWillReceiveProps
-    ⚛ AllLifecycles.shouldComponentUpdate
-    ⚛ AllLifecycles.componentWillUpdate
-    ⚛ AllLifecycles.getChildContext
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 2 Total)
-    ⚛ AllLifecycles.componentDidUpdate
-
-// Unmount
-⚛ (React Tree Reconciliation: Completed Root)
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-    ⚛ AllLifecycles.componentWillUnmount
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf deduplicates lifecycle names during commit to reduce overhead 1`] = `
-"// The commit phase should mention A and B just once
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⚛ A [update]
-    ⚛ B [update]
-    ⚛ A [update]
-    ⚛ B [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 9 Total)
-  ⚛ (Calling Lifecycle Methods: 9 Total)
-    ⚛ A.componentDidUpdate
-    ⚛ B.componentDidUpdate
-
-// Because of deduplication, we don't know B was cascading,
-// but we should still see the warning for the commit phase.
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⚛ A [update]
-    ⚛ B [update]
-    ⚛ A [update]
-    ⚛ B [update]
-
-⛔ (Committing Changes) Warning: Lifecycle hook scheduled a cascading update
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 9 Total)
-  ⚛ (Calling Lifecycle Methods: 9 Total)
-    ⚛ A.componentDidUpdate
-    ⚛ B.componentDidUpdate
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ B [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 2 Total)
-    ⚛ B.componentDidUpdate
-"
-`;
-
-exports[`ReactDebugFiberPerf does not include StrictMode or Profiler components in measurements 1`] = `
-"// Mount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Profiler [mount]
-    ⚛ Parent [mount]
-      ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf does not include context provider or consumer in measurements 1`] = `
-"// Mount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf does not schedule an extra callback if setState is called during a synchronous commit phase 1`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Component [mount]
-
-⛔ (Committing Changes) Warning: Lifecycle hook scheduled a cascading update
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-    ⛔ Component.componentDidMount Warning: Scheduled a cascading update
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Component [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf does not treat setState from cWM or cWRP as cascading 1`] = `
-"// Should not print a warning
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ NotCascading [mount]
-      ⚛ NotCascading.componentWillMount
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-// Should not print a warning
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⚛ NotCascading [update]
-      ⚛ NotCascading.componentWillReceiveProps
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 2 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf measures a simple reconciliation 1`] = `
-"// Mount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-// Update
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⚛ Child [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 2 Total)
-
-// Unmount
-⚛ (React Tree Reconciliation: Completed Root)
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf measures deferred work in chunks 1`] = `
-"// Start rendering through B
-⚛ (React Tree Reconciliation: Yielded)
-  ⚛ Parent [mount]
-    ⚛ A [mount]
-      ⚛ Child [mount]
-    ⚛ B [mount]
-
-// Complete the rest
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ B [mount]
-      ⚛ Child [mount]
-    ⚛ C [mount]
-      ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf measures deprioritized work 1`] = `
-"// Flush the parent
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-// Flush the child
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf properly displays the forwardRef component in measurements 1`] = `
-"// Mount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ ForwardRef [mount]
-      ⚛ Child [mount]
-    ⚛ ForwardRef(refForwarder) [mount]
-      ⚛ Child [mount]
-    ⚛ ForwardRef(OverriddenName) [mount]
-      ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf recovers from caught errors 1`] = `
-"// Stop on Baddie and restart from Boundary
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⛔ Boundary [mount] Warning: An error was thrown inside this error boundary
-      ⚛ Parent [mount]
-        ⚛ Baddie [mount]
-    ⚛ Boundary [mount]
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⛔ Boundary [mount] Warning: An error was thrown inside this error boundary
-      ⚛ Parent [mount]
-        ⚛ Baddie [mount]
-    ⚛ Boundary [mount]
-
-⛔ (Committing Changes) Warning: Lifecycle hook scheduled a cascading update
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Boundary [update]
-    ⚛ ErrorReport [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf recovers from fatal errors 1`] = `
-"// Will fatal
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Baddie [mount]
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Baddie [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-
-// Will reconcile from a clean state
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf skips parents during setState 1`] = `
-"// Should include just A and B, no Parents
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ A [update]
-  ⚛ B [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 2 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf supports Suspense and lazy 1`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Suspense [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf supports Suspense and lazy 2`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Suspense [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⛔ Suspense [update] Warning: Rendering was suspended
-    ⚛ Suspense [update]
-      ⚛ Spinner [mount]
-"
-`;
-
-exports[`ReactDebugFiberPerf supports Suspense and lazy 3`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Suspense [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⛔ Suspense [update] Warning: Rendering was suspended
-    ⚛ Suspense [update]
-      ⚛ Spinner [mount]
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [update]
-    ⚛ Suspense [update]
-      ⚛ Foo [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf supports memo 1`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Foo [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf supports portals 1`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf warns if an in-progress update is interrupted 1`] = `
-"⚛ (React Tree Reconciliation: Yielded)
-  ⚛ Foo [mount]
-
-⛔ (React Tree Reconciliation: Completed Root) Warning: A top-level update interrupted the previous render
-  ⚛ Foo [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-
-⚛ (React Tree Reconciliation: Completed Root)
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 0 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf warns if async work expires (starvation) 1`] = `
-"⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Foo [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf warns on cascading renders from setState 1`] = `
-"// Should print a warning
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Parent [mount]
-    ⚛ Cascading [mount]
-
-⛔ (Committing Changes) Warning: Lifecycle hook scheduled a cascading update
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 2 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-    ⛔ Cascading.componentDidMount Warning: Scheduled a cascading update
-
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Cascading [update]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-"
-`;
-
-exports[`ReactDebugFiberPerf warns on cascading renders from top-level render 1`] = `
-"// Rendering the first root
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Cascading [mount]
-
-⛔ (Committing Changes) Warning: Lifecycle hook scheduled a cascading update
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 1 Total)
-    ⛔ Cascading.componentDidMount Warning: Scheduled a cascading update
-
-// Scheduling another root from componentDidMount
-⚛ (React Tree Reconciliation: Completed Root)
-  ⚛ Child [mount]
-
-⚛ (Committing Changes)
-  ⚛ (Committing Snapshot Effects: 0 Total)
-  ⚛ (Committing Host Effects: 1 Total)
-  ⚛ (Calling Lifecycle Methods: 0 Total)
-"
-`;
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index 650e24529098..cc1688e076de 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -7,8 +7,6 @@
  * @flow strict
  */
 
-export const enableUserTimingAPI = __DEV__;
-
 // Helps identify side effects in render-phase lifecycle hooks and setState
 // reducers by double invoking them in Strict Mode.
 export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
@@ -39,11 +37,6 @@ export const enableBlocksAPI = __EXPERIMENTAL__;
 // Only used in www builds.
 export const enableSchedulerDebugging = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  throw new Error('Not implemented.');
-}
-
 // Disable javascript: URL strings in href for XSS protection.
 export const disableJavaScriptURLs = false;
 
diff --git a/packages/shared/forks/ReactFeatureFlags.native-fb.js b/packages/shared/forks/ReactFeatureFlags.native-fb.js
index c70c777cfd9c..10f458679512 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-fb.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-fb.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.native-fb';
 
 // The rest of the flags are static for better dead code elimination.
-export const enableUserTimingAPI = __DEV__;
 export const enableProfilerTimer = __PROFILE__;
 export const enableProfilerCommitHooks = false;
 export const enableSchedulerTracing = __PROFILE__;
@@ -54,11 +51,6 @@ export const throwEarlyForMysteriousError = true;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.native-oss.js b/packages/shared/forks/ReactFeatureFlags.native-oss.js
index 61527ea6db69..2c01721d51d9 100644
--- a/packages/shared/forks/ReactFeatureFlags.native-oss.js
+++ b/packages/shared/forks/ReactFeatureFlags.native-oss.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.native-oss';
 
 export const debugRenderPhaseSideEffectsForStrictMode = false;
-export const enableUserTimingAPI = __DEV__;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const warnAboutDeprecatedLifecycles = true;
 export const enableProfilerTimer = __PROFILE__;
@@ -53,11 +50,6 @@ export const throwEarlyForMysteriousError = false;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
index ffc66b7acc8a..4ca1a4a381e6 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.test-renderer';
 
 export const debugRenderPhaseSideEffectsForStrictMode = false;
-export const enableUserTimingAPI = __DEV__;
 export const warnAboutDeprecatedLifecycles = true;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = __PROFILE__;
@@ -53,11 +50,6 @@ export const throwEarlyForMysteriousError = false;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
index 6734118d0a77..85859e15ffb5 100644
--- a/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.test-renderer.www.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.test-renderer.www';
 
 export const debugRenderPhaseSideEffectsForStrictMode = false;
-export const enableUserTimingAPI = __DEV__;
 export const warnAboutDeprecatedLifecycles = true;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = __PROFILE__;
@@ -53,11 +50,6 @@ export const throwEarlyForMysteriousError = false;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.testing.js b/packages/shared/forks/ReactFeatureFlags.testing.js
index 6b279bc8a6a3..88386e30a679 100644
--- a/packages/shared/forks/ReactFeatureFlags.testing.js
+++ b/packages/shared/forks/ReactFeatureFlags.testing.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.testing';
 
 export const debugRenderPhaseSideEffectsForStrictMode = false;
-export const enableUserTimingAPI = __DEV__;
 export const warnAboutDeprecatedLifecycles = true;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = __PROFILE__;
@@ -53,11 +50,6 @@ export const throwEarlyForMysteriousError = false;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.testing.www.js b/packages/shared/forks/ReactFeatureFlags.testing.www.js
index afdacac78719..0e01547c769f 100644
--- a/packages/shared/forks/ReactFeatureFlags.testing.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.testing.www.js
@@ -7,13 +7,10 @@
  * @flow
  */
 
-import invariant from 'shared/invariant';
-
 import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
 import typeof * as ExportsType from './ReactFeatureFlags.testing.www';
 
 export const debugRenderPhaseSideEffectsForStrictMode = false;
-export const enableUserTimingAPI = false;
 export const warnAboutDeprecatedLifecycles = true;
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = false;
@@ -53,11 +50,6 @@ export const throwEarlyForMysteriousError = false;
 
 export const enableNewReconciler = false;
 
-// Only used in www builds.
-export function addUserTimingListener() {
-  invariant(false, 'Not implemented.');
-}
-
 // Flow magic to verify the exports of this file match the original version.
 // eslint-disable-next-line no-unused-vars
 type Check<_X, Y: _X, X: Y = _X> = null;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index d424e40b3dfb..5190aa0d4d4b 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -30,14 +30,6 @@ export const {
 // On WWW, __EXPERIMENTAL__ is used for a new modern build.
 // It's not used anywhere in production yet.
 
-// In www, we have experimental support for gathering data
-// from User Timing API calls in production. By default, we
-// only emit performance.mark/measure calls in __DEV__. But if
-// somebody calls addUserTimingListener() which is exposed as an
-// experimental FB-only export, we call performance.mark/measure
-// as long as there is more than a single listener.
-export let enableUserTimingAPI = __DEV__ && !__EXPERIMENTAL__;
-
 export const enableProfilerTimer = __PROFILE__;
 export const enableProfilerCommitHooks = __PROFILE__;
 
@@ -59,33 +51,6 @@ export const enableBlocksAPI = true;
 
 export const disableJavaScriptURLs = true;
 
-let refCount = 0;
-export function addUserTimingListener() {
-  if (__DEV__) {
-    // Noop.
-    return () => {};
-  }
-  refCount++;
-  updateFlagOutsideOfReactCallStack();
-  return () => {
-    refCount--;
-    updateFlagOutsideOfReactCallStack();
-  };
-}
-
-// The flag is intentionally updated in a timeout.
-// We don't support toggling it during reconciliation or
-// commit since that would cause mismatching user timing API calls.
-let timeout = null;
-function updateFlagOutsideOfReactCallStack() {
-  if (!timeout) {
-    timeout = setTimeout(() => {
-      timeout = null;
-      enableUserTimingAPI = refCount > 0;
-    });
-  }
-}
-
 export const enableDeprecatedFlareAPI = true;
 
 export const enableFundamentalAPI = false;
diff --git a/scripts/jest/setupTests.www.js b/scripts/jest/setupTests.www.js
index f57f2b383e30..73a3f8769475 100644
--- a/scripts/jest/setupTests.www.js
+++ b/scripts/jest/setupTests.www.js
@@ -15,7 +15,6 @@ jest.mock('shared/ReactFeatureFlags', () => {
   // configuration, too. Then remove these overrides.
   wwwFlags.disableLegacyContext = defaultFlags.disableLegacyContext;
   wwwFlags.warnAboutUnmockedScheduler = defaultFlags.warnAboutUnmockedScheduler;
-  wwwFlags.enableUserTimingAPI = defaultFlags.enableUserTimingAPI;
   wwwFlags.disableJavaScriptURLs = defaultFlags.disableJavaScriptURLs;
   wwwFlags.enableDeprecatedFlareAPI = defaultFlags.enableDeprecatedFlareAPI;
   wwwFlags.disableModulePatternComponents =