From 76d4b180d016d6bab10602e8b47100bc4bc0e6fd Mon Sep 17 00:00:00 2001
From: Ruihan Li <lrh2000@pku.edu.cn>
Date: Mon, 30 Sep 2024 16:03:46 +0800
Subject: [PATCH] Increase the TCP socket buffer length

---
 .../libs/aster-bigtcp/src/socket/unbound.rs   | 20 +++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/kernel/libs/aster-bigtcp/src/socket/unbound.rs b/kernel/libs/aster-bigtcp/src/socket/unbound.rs
index 97de13c6e..b79f60bba 100644
--- a/kernel/libs/aster-bigtcp/src/socket/unbound.rs
+++ b/kernel/libs/aster-bigtcp/src/socket/unbound.rs
@@ -53,11 +53,23 @@ impl<T> UnboundSocket<T> {
     }
 }
 
-// For TCP
-pub const TCP_RECV_BUF_LEN: usize = 65536;
-pub const TCP_SEND_BUF_LEN: usize = 65536;
+// TCP socket buffer sizes:
+//
+// According to
+// <https://github.com/torvalds/linux/blob/9852d85ec9d492ebef56dc5f229416c925758edc/include/net/sock.h#L2798-L2806>
+// and
+// <https://github.com/torvalds/linux/blob/9852d85ec9d492ebef56dc5f229416c925758edc/net/core/sock.c#L286-L287>,
+// it seems that the socket buffer should be 256 packets * 256 bytes/packet = 65536 bytes by
+// default. However, the loopback MTU is also 65536 bytes, and having the same size for the socket
+// buffer and the MTU will cause the implementation of Nagle's algorithm in smoltcp to behave
+// abnormally (see <https://github.com/asterinas/asterinas/pull/1396>). So the socket buffer size
+// is increased from 64K to 128K.
+//
+// TODO: Consider allowing user programs to set the socket buffer length via `setsockopt` system calls.
+pub const TCP_RECV_BUF_LEN: usize = 65536 * 2;
+pub const TCP_SEND_BUF_LEN: usize = 65536 * 2;
 
-// For UDP
+// UDP socket buffer sizes:
 pub const UDP_SEND_PAYLOAD_LEN: usize = 65536;
 pub const UDP_RECV_PAYLOAD_LEN: usize = 65536;
 const UDP_METADATA_LEN: usize = 256;