From f5f5ee31a25e37d6a19939f837f0089431f9951c Mon Sep 17 00:00:00 2001
From: Ara Ayvazyan <Aivazyan@microsoft.com>
Date: Thu, 26 Apr 2018 16:23:06 -0700
Subject: [PATCH] Enable SIO_LOOPBACK_FAST_PATH on Windows

---
 src/core/lib/iomgr/tcp_windows.cc | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/core/lib/iomgr/tcp_windows.cc b/src/core/lib/iomgr/tcp_windows.cc
index 04e6f11eeeb..5d316d477b7 100644
--- a/src/core/lib/iomgr/tcp_windows.cc
+++ b/src/core/lib/iomgr/tcp_windows.cc
@@ -74,12 +74,28 @@ static grpc_error* set_dualstack(SOCKET sock) {
              : GRPC_WSA_ERROR(WSAGetLastError(), "setsockopt(IPV6_V6ONLY)");
 }
 
+static grpc_error* enable_loopback_fast_path(SOCKET sock) {
+  int status;
+  uint32_t param = 1;
+  DWORD ret;
+  status = WSAIoctl(sock, /*SIO_LOOPBACK_FAST_PATH==*/_WSAIOW(IOC_VENDOR, 16),
+                    &param, sizeof(param), NULL, 0, &ret, 0, 0);
+  if (status == SOCKET_ERROR) {
+    status = WSAGetLastError();
+  }
+  return status == 0 || status == WSAEOPNOTSUPP
+             ? GRPC_ERROR_NONE
+             : GRPC_WSA_ERROR(status, "WSAIoctl(SIO_LOOPBACK_FAST_PATH)");
+}
+
 grpc_error* grpc_tcp_prepare_socket(SOCKET sock) {
   grpc_error* err;
   err = set_non_block(sock);
   if (err != GRPC_ERROR_NONE) return err;
   err = set_dualstack(sock);
   if (err != GRPC_ERROR_NONE) return err;
+  err = enable_loopback_fast_path(sock);
+  if (err != GRPC_ERROR_NONE) return err;
   return GRPC_ERROR_NONE;
 }