Be more lazy about stream flow control updates

src/core/ext/transport/chttp2/transport/parsing.c

@@ -375,9 +375,14 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
     return err;
   }
 
+  uint32_t target_incoming_window = GPR_MAX(
+      t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
+      1024);
   GRPC_CHTTP2_FLOW_DEBIT_TRANSPORT("parse", t, incoming_window,
                                    incoming_frame_size);
+  if (t->incoming_window < target_incoming_window / 2) {
     grpc_chttp2_initiate_write(exec_ctx, t, false, "flow_control");
+  }
 
   if (s != NULL) {
     if (incoming_frame_size >

src/core/ext/transport/chttp2/transport/writing.c

@@ -295,7 +295,10 @@ bool grpc_chttp2_begin_write(grpc_exec_ctx *exec_ctx,
   uint32_t target_incoming_window = GPR_MAX(
       t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
       1024);
-  if (t->incoming_window < 3 * target_incoming_window / 4) {
+  uint32_t threshold_to_send_transport_window_update =
+      t->outbuf.count > 0 ? target_incoming_window
+                          : 3 * target_incoming_window / 4;
+  if (t->incoming_window < threshold_to_send_transport_window_update) {
     maybe_initiate_ping(exec_ctx, t,
                         GRPC_CHTTP2_PING_BEFORE_TRANSPORT_WINDOW_UPDATE);
     uint32_t announced = (uint32_t)GPR_CLAMP(