Only filter if it's a retrigger command.

src/EditorFeatures/Core/Implementation/IntelliSense/SignatureHelp/Controller.Session.cs

@@ -9,10 +9,14 @@ internal partial class Controller
     {
         internal partial class Session : Session<Controller, Model, ISignatureHelpPresenterSession>
         {
-            // When we issue compute tasks, provide them with a (monotonically increasing) id.  That
-            // way, when they run we can bail on computation if they've been superseded by another
-            // compute task.
-            private int _computeId;
+            /// <summary>
+            /// When ther user moves the caret we issue retrigger commands.  There may be a long
+            /// chain of these, and they may take time for each to process.  This can be visible 
+            /// to the user as a long delay before the signature help items update.  To avoid this
+            /// we keep track if there is new outstanding retrigger command and we bail on the
+            /// computation if another is in the queue.
+            /// </summary>
+            private int _retriggerId;
 
             public Session(Controller controller, ISignatureHelpPresenterSession presenterSession)
                 : base(controller, new ModelComputation<Model>(controller, TaskScheduler.Default), presenterSession)

src/EditorFeatures/Core/Implementation/IntelliSense/SignatureHelp/Controller.Session_ComputeModel.cs

@@ -39,8 +39,12 @@ internal partial class Session
                 var caretPosition = Controller.TextView.GetCaretPoint(Controller.SubjectBuffer).Value;
                 var disconnectedBufferGraph = new DisconnectedBufferGraph(Controller.SubjectBuffer, Controller.TextView.TextBuffer);
 
-                Interlocked.Increment(ref _computeId);
-                var localId = _computeId;
+                if (triggerInfo.TriggerReason == SignatureHelpTriggerReason.RetriggerCommand)
+                {
+                    Interlocked.Increment(ref _retriggerId);
+                }
+
+                var localId = _retriggerId;
 
                 // If we've already computed a model, then just use that.  Otherwise, actually
                 // compute a new model and send that along.
@@ -196,7 +200,8 @@ private static bool CompareParts(TaggedText p1, TaggedText p2)
                     // to the extension crashing.
                     foreach (var provider in providers)
                     {
-                        if (id != _computeId)
+                        if (triggerInfo.TriggerReason == SignatureHelpTriggerReason.RetriggerCommand &&
+                            id != _retriggerId)
                         {
                             return (null, null);
                         }

src/EditorFeatures/Core/Implementation/IntelliSense/SignatureHelp/Controller_TypeChar.cs

@@ -71,9 +71,7 @@ void ICommandHandler<TypeCharCommandArgs>.ExecuteCommand(TypeCharCommandArgs arg
             // care of cases where the filtered set of providers didn't provide anything but one of the
             // other providers could still be valid, but doesn't explicitly treat the typed character as
             // a trigger character.
-            var filteredProviders = FilterProviders(allProviders, args.TypedChar);
-            var textuallyTriggeredProviders = filteredProviders.Item1;
-            var untriggeredProviders = filteredProviders.Item2;
+            var (textuallyTriggeredProviders, untriggeredProviders) = FilterProviders(allProviders, args.TypedChar);
             var triggerInfo = new SignatureHelpTriggerInfo(SignatureHelpTriggerReason.TypeCharCommand, args.TypedChar);
 
             if (!IsSessionActive)