net/tcp: Re-think CONFIG_NET_TCP_RWND_CONTROL TCP windowing controls.

include/nuttx/mm/iob.h

@@ -1,7 +1,7 @@
 /****************************************************************************
  * include/nuttx/mm/iob.h
  *
- *   Copyright (C) 2014 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2014, 2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -183,6 +183,16 @@ FAR struct iob_s *iob_alloc(bool throttled);
 
 FAR struct iob_s *iob_tryalloc(bool throttled);
 
+/****************************************************************************
+ * Name: iob_navail
+ *
+ * Description:
+ *   Return the number of of available IOBs.
+ *
+ ****************************************************************************/
+
+int iob_navail(void);
+
 /****************************************************************************
  * Name: iob_free
  *

mm/iob/Make.defs

@@ -1,7 +1,7 @@
 ############################################################################
 # mm/iob/Make.defs
 #
-#   Copyright (C) 2014, 2017 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2014, 2017-2018 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -42,6 +42,7 @@ CSRCS += iob_concat.c iob_copyin.c iob_copyout.c iob_contig.c iob_free.c
 CSRCS += iob_free_chain.c iob_free_qentry.c iob_free_queue.c
 CSRCS += iob_initialize.c iob_pack.c iob_peek_queue.c iob_remove_queue.c
 CSRCS += iob_trimhead.c iob_trimhead_queue.c iob_trimtail.c
+CSRCS += iob_navail.c
 
 ifeq ($(CONFIG_DEBUG_FEATURES),y)
   CSRCS += iob_dump.c

mm/iob/iob_navail.c

@@ -0,0 +1,71 @@
+/****************************************************************************
+ * mm/iob/iob_navail.c
+ *
+ *   Copyright (C) 2018 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <nuttx/semaphore.h>
+#include <nuttx/mm/iob.h>
+
+#include "iob.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: iob_navail
+ *
+ * Description:
+ *   Return the number of of available IOBs.
+ *
+ ****************************************************************************/
+
+int iob_navail(void)
+{
+  int navail = 0;
+  int ret;
+
+  ret = nxsem_getvalue(&g_qentry_sem, &navail);
+  if (ret >= 0)
+    {
+      ret = navail;
+    }
+
+  return ret;
+}

net/Kconfig

@@ -61,12 +61,17 @@ config NET_ETH_TCP_RECVWNDO
 	default 1220 if NET_IPv6
 	default 536 if !NET_IPv6
 	depends on NET_ETHERNET && NET_TCP
+	range 536 65535
 	---help---
 		The size of the advertised receiver's window.   Should be set low
 		(i.e., to the size of the MSS) if the application is slow to process
-		incoming data, or high (32768 bytes) if the application processes
+		incoming data, or high (65,535 bytes) if the application processes
 		data quickly.
 
+		This value does not account for buffering provided for read-ahead
+		buffering via IOBs.  To include IOB aware windowing logic also
+		enable CONFIG_NET_TCP_RWND_CONTROL.
+
 config NET_SLIP_MTU
 	int # "SLIP packet buffer size (MTU)"
 	default 296

net/tcp/Kconfig

@@ -178,9 +178,12 @@ endif # NET_TCP && !NET_TCP_NO_STACK
 config NET_TCP_RWND_CONTROL
 	bool "Receive window control based on IOBuffer"
 	default n
-	depends on MM_IOB
+	depends on NET_READAHEAD
 	---help---
 		Support receive window control based on I/O buffer.  This feature
 		is still experimental.
 
+		This feature, if enabled, will assume that the every IOB is
+		available for read-ahead storage of TCP packets.
+
 endmenu # TCP/IP Networking

net/tcp/tcp_send.c

@@ -1,7 +1,8 @@
 /****************************************************************************
  * net/tcp/tcp_send.c
  *
- *   Copyright (C) 2007-2010, 2012, 2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2010, 2012, 2015, 2018 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Adapted for NuttX from logic in uIP which also has a BSD-like license:
@@ -314,9 +315,10 @@ static void tcp_sendcommon(FAR struct net_driver_s *dev,
                            FAR struct tcp_hdr_s *tcp)
 {
 #ifdef CONFIG_NET_TCP_RWND_CONTROL
-  extern sem_t g_qentry_sem;
-  int  qentry_sem_count;
   uint32_t rwnd;
+  uint16_t iplen;
+  uint16_t overhead;
+  int  navail;
 #endif
 
   /* Copy the IP address into the IPv6 header */
@@ -327,8 +329,13 @@ static void tcp_sendcommon(FAR struct net_driver_s *dev,
 #endif
     {
       FAR struct ipv6_hdr_s *ipv6 = IPv6BUF;
+
       net_ipv6addr_hdrcopy(ipv6->srcipaddr, dev->d_ipv6addr);
       net_ipv6addr_hdrcopy(ipv6->destipaddr, conn->u.ipv6.raddr);
+
+#ifdef CONFIG_NET_TCP_RWND_CONTROL
+      iplen = IPv6_HDRLEN;
+#endif
     }
 #endif /* CONFIG_NET_IPv6 */
 
@@ -338,8 +345,13 @@ static void tcp_sendcommon(FAR struct net_driver_s *dev,
 #endif
     {
       FAR struct ipv4_hdr_s *ipv4 = IPv4BUF;
+
       net_ipv4addr_hdrcopy(ipv4->srcipaddr, &dev->d_ipaddr);
       net_ipv4addr_hdrcopy(ipv4->destipaddr, &conn->u.ipv4.raddr);
+
+#ifdef CONFIG_NET_TCP_RWND_CONTROL
+      iplen = IPv4_HDRLEN;
+#endif
     }
 #endif /* CONFIG_NET_IPv4 */
 
@@ -352,16 +364,64 @@ static void tcp_sendcommon(FAR struct net_driver_s *dev,
   tcp->destport = conn->rport;
 
 #ifdef CONFIG_NET_TCP_RWND_CONTROL
-  /* Update the TCP received window based on I/O buffer */
+  /* Update the TCP received window based on I/O buffer availability */
   /* NOTE: This algorithm is still experimental */
 
-  if (OK == nxsem_getvalue(&g_qentry_sem, &qentry_sem_count))
+  overhead = NET_LL_HDRLEN(dev) + iplen + TCP_HDRLEN;
+  navail   = iob_navail();
+  if (navail > 0)
     {
-      rwnd = (qentry_sem_count * CONFIG_NET_ETH_TCP_RECVWNDO)
+      /* The optimal TCP window size is the amount of TCP data that we can
-             / CONFIG_IOB_NCHAINS;
+       * currently buffer via TCP read-ahead buffering minus overhead for the
+       * link-layer, IP, and TCP headers.  This logic here assumes that
+       * all IOBs are available for TCP buffering.
+       *
+       * REVISIT:  In an environment with mutliple, active read-ahead TCP
+       * sockets (and perhaps multiple network devices) or if there are
+       * other consumers of IOBs (such as for TCP write buffering) then the
+       * total number of IOBs will all not be available for read-ahead
+       * buffering for this connection.
+       */
+
+#if 0
+      /* REVISIT:  (1)CONFIG_NET_ETH_TCP_RECVWNDO will typically be larger
+       * than the IOB payload size.  (2) Why divide by CONFIG_IOB_NCHAINS?
+       * (3) CONFIG_NET_ETH_TCP_RECVWNDO includes the header overhead
+       * penalty.  But we only have to pay the header overhead penalty
+       * once.  (4) This logic needs to work even if Ethernet is not
+       * enabled (and hence CONFIG_NET_ETH_TCP_RECVWNDO is not defined).
+       */
+
+      rwnd = (navail * CONFIG_NET_ETH_TCP_RECVWNDO) / CONFIG_IOB_NCHAINS;
+#else
+      /* Assume that all of the available IOBs are can be used for buffering
+       * on this connection.
+       */
+
+      rwnd = (navail * CONFIG_IOB_BUFSIZE) - overhead;
+#endif
+
+      /* Save the new receive window size */
+
+      if (rwnd > UINT16_MAX)
+        {
+          rwnd = UINT16_MAX;
+        }
 
       NET_DEV_RCVWNDO(dev) = (uint16_t)rwnd;
     }
+  else /* (navail == 0) */
+    {
+      /* No IOBs are available... fall back to the configured default
+       * which assumes no write buffering.  The only buffering available
+       * is the packet itself.
+       *
+       * NOTE:  If no IOBs are available, then the next packet will be
+       * lost will be be lost if there is no listener on the connection.
+       */
+
+      NET_DEV_RCVWNDO(dev) = dev->d_mtu - overhead;
+    }
 #endif
 
   /* Set the TCP window */