[Performance]net/tcp: send the ACK in time after obtain ahead buffer from iobs

Request the TCP ACK to estimate the receive window after handle
any data already buffered in a read-ahead buffer.

Change-Id: Id998a1125dd2991d73ba4bef081ddcb7adea4f0d
Signed-off-by: chao.an <anchao@xiaomi.com>

net/tcp/tcp.h

@@ -273,6 +273,12 @@ struct tcp_conn_s
 
   FAR struct devif_callback_s *connevents;
 
+  /* Receiver callback to indicate that the data has been consumed and that
+   * an ACK should be send.
+   */
+
+  FAR struct devif_callback_s *rcv_ackcb;
+
   /* accept() is called when the TCP logic has created a connection
    *
    *   accept_private: This is private data that will be available to the

net/tcp/tcp_recvfrom.c

@@ -365,7 +365,7 @@ static inline void tcp_sender(FAR struct net_driver_s *dev,
 }
 
 /****************************************************************************
- * Name: tcp_eventhandler
+ * Name: tcp_recvhandler
  *
  * Description:
  *   This function is called with the network locked to perform the actual
@@ -384,7 +384,7 @@ static inline void tcp_sender(FAR struct net_driver_s *dev,
  *
  ****************************************************************************/
 
-static uint16_t tcp_eventhandler(FAR struct net_driver_s *dev,
+static uint16_t tcp_recvhandler(FAR struct net_driver_s *dev,
                                 FAR void *pvconn, FAR void *pvpriv,
                                 uint16_t flags)
 {
@@ -510,6 +510,53 @@ static uint16_t tcp_eventhandler(FAR struct net_driver_s *dev,
   return flags;
 }
 
+/****************************************************************************
+ * Name: tcp_ackhandler
+ *
+ * Description:
+ *   This function is called with the network locked to send the ACK in
+ *   response by the lower, device interfacing layer.
+ *
+ * Input Parameters:
+ *   dev      The structure of the network driver that generated the event.
+ *   pvconn   The connection structure associated with the socket
+ *   flags    Set of events describing why the callback was invoked
+ *
+ * Returned Value:
+ *   ACK should be send in the response.
+ *
+ * Assumptions:
+ *   The network is locked.
+ *
+ ****************************************************************************/
+
+static uint16_t tcp_ackhandler(FAR struct net_driver_s *dev,
+                               FAR void *pvconn, FAR void *pvpriv,
+                               uint16_t flags)
+{
+  FAR struct tcp_conn_s *conn = (FAR struct tcp_conn_s *)pvconn;
+
+  ninfo("flags: %04x\n", flags);
+
+  if (conn != NULL && (flags & TCP_POLL) != 0)
+    {
+      /* Indicate that the data has been consumed and that an ACK
+       * should be send.
+       */
+
+      if (tcp_get_recvwindow(dev, conn) != 0 &&
+          conn->rcv_wnd == 0)
+        {
+          flags |= TCP_SNDACK;
+        }
+
+      tcp_callback_free(conn, conn->rcv_ackcb);
+      conn->rcv_ackcb = NULL;
+    }
+
+  return flags;
+}
+
 /****************************************************************************
  * Name: tcp_recvfrom_initialize
  *
@@ -637,13 +684,17 @@ ssize_t psock_tcp_recvfrom(FAR struct socket *psock, FAR void *buf,
                            FAR socklen_t *fromlen)
 {
   struct tcp_recvfrom_s  state;
+  FAR struct tcp_conn_s *conn;
   int                    ret;
 
+  net_lock();
+
+  conn = (FAR struct tcp_conn_s *)psock->s_conn;
+
   /* Initialize the state structure.  This is done with the network locked
    * because we don't want anything to happen until we are ready.
    */
 
-  net_lock();
   tcp_recvfrom_initialize(psock, buf, len, from, fromlen, &state);
 
   /* Handle any any TCP data already buffered in a read-ahead buffer.  NOTE
@@ -727,8 +778,6 @@ ssize_t psock_tcp_recvfrom(FAR struct socket *psock, FAR void *buf,
 
   if (state.ir_recvlen == 0 && state.ir_buflen > 0)
     {
-      FAR struct tcp_conn_s *conn = (FAR struct tcp_conn_s *)psock->s_conn;
-
       /* Set up the callback in the connection */
 
       state.ir_cb = tcp_callback_alloc(conn);
@@ -736,7 +785,7 @@ ssize_t psock_tcp_recvfrom(FAR struct socket *psock, FAR void *buf,
         {
           state.ir_cb->flags   = (TCP_NEWDATA | TCP_DISCONN_EVENTS);
           state.ir_cb->priv    = (FAR void *)&state;
-          state.ir_cb->event   = tcp_eventhandler;
+          state.ir_cb->event   = tcp_recvhandler;
 
           /* Wait for either the receive to complete or for an error/timeout
            * to occur.  net_timedwait will also terminate if a signal isi
@@ -760,6 +809,20 @@ ssize_t psock_tcp_recvfrom(FAR struct socket *psock, FAR void *buf,
         }
     }
 
+  /* Receive additional data from read-ahead buffer, send the ACK timely. */
+
+  else if (state.ir_recvlen > 0 && conn->rcv_wnd == 0 &&
+           conn->rcv_ackcb == NULL)
+    {
+      conn->rcv_ackcb = tcp_callback_alloc(conn);
+      if (conn->rcv_ackcb)
+        {
+          conn->rcv_ackcb->flags   = TCP_POLL;
+          conn->rcv_ackcb->event   = tcp_ackhandler;
+          netdev_txnotify_dev(conn->dev);
+        }
+    }
+
   net_unlock();
   tcp_recvfrom_uninitialize(&state);
   return (ssize_t)ret;