Refine flow control update rules: drastic improvement in trickle failure rates

src/core/ext/transport/chttp2/transport/chttp2_transport.c

@@ -2542,7 +2542,7 @@ static void incoming_byte_stream_update_flow_control(grpc_exec_ctx *exec_ctx,
                                    add_max_recv_bytes);
     if ((int64_t)s->incoming_window_delta + (int64_t)initial_window_size -
             (int64_t)s->announce_window >
-        (int64_t)initial_window_size / 2) {
+        2 * (int64_t)initial_window_size) {
       write_type = GRPC_CHTTP2_STREAM_WRITE_PIGGYBACK;
     }
     grpc_chttp2_become_writable(exec_ctx, t, s, write_type,

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

@@ -418,12 +418,7 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
 
     GRPC_CHTTP2_FLOW_DEBIT_STREAM_INCOMING_WINDOW_DELTA("parse", t, s,
                                                         incoming_frame_size);
-    if ((int64_t)t->settings[GRPC_SENT_SETTINGS]
+    if ((int64_t)s->incoming_window_delta - (int64_t)s->announce_window <= 0) {
-                            [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] +
-            (int64_t)s->incoming_window_delta - (int64_t)s->announce_window <=
-        (int64_t)t->settings[GRPC_SENT_SETTINGS]
-                            [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] /
-            2) {
       grpc_chttp2_become_writable(exec_ctx, t, s,
                                   GRPC_CHTTP2_STREAM_WRITE_INITIATE_UNCOVERED,
                                   "window-update-required");