New setting EnableKernelResponseBuffering to improve response write throughput

Author: davidni

src/Microsoft.Net.Http.Server/RequestProcessing/ResponseStream.cs

@@ -42,6 +42,8 @@ internal RequestContext RequestContext
 
         internal bool ThrowWriteExceptions => RequestContext.Server.Settings.ThrowWriteExceptions;
 
+        internal bool EnableKernelResponseBuffering => RequestContext.Server.Settings.EnableKernelResponseBuffering;
+
         internal bool IsDisposed => _disposed;
 
         public override bool CanSeek
@@ -431,6 +433,10 @@ private HttpApi.HTTP_FLAGS ComputeLeftToWrite(long writeCount, bool endOfRequest
             else if (!endOfRequest && _leftToWrite != writeCount)
             {
                 flags |= HttpApi.HTTP_FLAGS.HTTP_SEND_RESPONSE_FLAG_MORE_DATA;
+                if (EnableKernelResponseBuffering)
+                {
+                    flags |= HttpApi.HTTP_FLAGS.HTTP_SEND_RESPONSE_FLAG_BUFFER_DATA;
+                }
             }
 
             // Update _leftToWrite now so we can queue up additional async writes.

src/Microsoft.Net.Http.Server/WebListenerSettings.cs

@@ -61,6 +61,15 @@ public ILogger Logger
         /// </summary>
         public bool ThrowWriteExceptions { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value that indicates whether to enable buffering of data in the kernel on a per-response basis.
+        /// It should be used by an application doing synchronous I/O or by an application doing asynchronous I/O with
+        /// no more than one outstanding send at a time.
+        /// Applications that use asynchronous I/O and that may have more than one send outstanding at a time should not use this flag.
+        /// Enabling this can results in higher CPU and memory usage by Http.Sys.
+        /// </summary>
+        public bool EnableKernelResponseBuffering { get; set; }
+
         /// <summary>
         /// Gets or sets the maximum number of requests that will be queued up in Http.Sys.
         /// </summary>