add separate variables for connection window update for fine tunning the performance of flow control; set initial connection window size to 1MB which is used in Java and C also

transport/control.go

@@ -42,10 +42,12 @@ import (
 // TODO(zhaoq): Make the following configurable.
 const (
 	// The initial window size for flow control.
-	initialWindowSize = 65535
+	initialWindowSize = 65535  // for an RPC
+	initialConnWindowSize = 1024 * 1024  // for a connection
 	// Window update is only sent when the inbound quota reaches
 	// this threshold. Used to reduce the flow control traffic.
-	windowUpdateThreshold = 16384
+	windowUpdateThreshold = 16384  // for an RPC
+	connWindowUpdateThreshold = 1024 * 256  // for a connection
 )
 
 // The following defines various control items which could flow through

transport/http2_client.go

@@ -149,7 +149,7 @@ func newHTTP2Client(addr string, opts *DialOptions) (_ ClientTransport, err erro
 		hBuf:          &buf,
 		hEnc:          hpack.NewEncoder(&buf),
 		controlBuf:    newRecvBuffer(),
-		sendQuotaPool: newQuotaPool(initialWindowSize),
+		sendQuotaPool: newQuotaPool(initialConnWindowSize),
 		scheme:        scheme,
 		state:         reachable,
 		activeStreams: make(map[uint32]*Stream),
@@ -457,11 +457,11 @@ func (t *http2Client) getStream(f http2.Frame) (*Stream, bool) {
 
 // addRecvQuota adjusts the inbound quota for the stream and the transport.
 // Window updates will deliver to the controller for sending when
-// the cumulative quota exceeds windowUpdateThreshold.
+// the cumulative quota exceeds the corresponding threshold.
 func (t *http2Client) addRecvQuota(s *Stream, n int) {
 	t.mu.Lock()
 	t.recvQuota += n
-	if t.recvQuota >= windowUpdateThreshold {
+	if t.recvQuota >= connWindowUpdateThreshold {
 		t.controlBuf.put(&windowUpdate{0, uint32(t.recvQuota)})
 		t.recvQuota = 0
 	}

transport/http2_server.go

@@ -109,7 +109,7 @@ func newHTTP2Server(conn net.Conn, maxStreams uint32) (_ ServerTransport, err er
 		hEnc:          hpack.NewEncoder(&buf),
 		maxStreams:    maxStreams,
 		controlBuf:    newRecvBuffer(),
-		sendQuotaPool: newQuotaPool(initialWindowSize),
+		sendQuotaPool: newQuotaPool(initialConnWindowSize),
 		state:         reachable,
 		writableChan:  make(chan int, 1),
 		shutdownChan:  make(chan struct{}),
@@ -284,11 +284,11 @@ func (t *http2Server) getStream(f http2.Frame) (*Stream, bool) {
 
 // addRecvQuota adjusts the inbound quota for the stream and the transport.
 // Window updates will deliver to the controller for sending when
-// the cumulative quota exceeds windowUpdateThreshold.
+// the cumulative quota exceeds the corresponding threshold.
 func (t *http2Server) addRecvQuota(s *Stream, n int) {
 	t.mu.Lock()
 	t.recvQuota += n
-	if t.recvQuota >= windowUpdateThreshold {
+	if t.recvQuota >= connWindowUpdateThreshold {
 		t.controlBuf.put(&windowUpdate{0, uint32(t.recvQuota)})
 		t.recvQuota = 0
 	}