Doc http.sys response buffering option (#29649)

aspnetcore/fundamentals/servers/httpsys.md

@@ -5,7 +5,7 @@ description: Learn about HTTP.sys, a web server for ASP.NET Core on Windows. Bui
 monikerRange: '>= aspnetcore-2.1'
 ms.author: riande
 ms.custom: mvc
-ms.date: 6/17/2023
+ms.date: 06/26/2023
 uid: fundamentals/servers/httpsys
 ---
 # HTTP.sys web server implementation in ASP.NET Core
@@ -90,6 +90,14 @@ Http.Sys also supports sending an AltSvc HTTP/2 protocol message rather than a r
 
 HTTP.sys delegates to kernel mode authentication with the Kerberos authentication protocol. User mode authentication isn't supported with Kerberos and HTTP.sys. The machine account must be used to decrypt the Kerberos token/ticket that's obtained from Active Directory and forwarded by the client to the server to authenticate the user. Register the Service Principal Name (SPN) for the host, not the user of the app.
 
+### Support for kernel-mode response buffering
+
+In some scenarios, high volumes of small writes with high latency can cause significant performance impact to `HTTP.sys`. This impact is due to the lack of a <xref:System.IO.Pipelines.Pipe> buffer in the `HTTP.sys` implementation. To improve performance in these scenarios, support for response buffering is included in `HTTP.sys`. Enable buffering by setting [HttpSysOptions.EnableKernelResponseBuffering](https://github.com/dotnet/aspnetcore/blob/main/src/Servers/HttpSys/src/HttpSysOptions.cs#L120) to `true`.
+
+Response buffering should be enabled by an app that does synchronous I/O, or asynchronous I/O with no more than one outstanding write at a time. In these scenarios, response buffering can significantly improve throughput over high-latency connections.
+
+Apps that use asynchronous I/O and that may have more than one write outstanding at a time should **_not_** use this flag. Enabling this flag can result in higher CPU and memory usage by HTTP.Sys.
+
 ## How to use HTTP.sys
 
 ### Configure the ASP.NET Core app to use HTTP.sys