From aac36757d44cd69bc0122d67bc48e9b8e9b2b6cb Mon Sep 17 00:00:00 2001
From: zonyitoo <zonyitoo@gmail.com>
Date: Wed, 26 Mar 2025 00:36:35 +0800
Subject: [PATCH] feat(local-tun): disable receive checksum, improving
 performance

- ref #1923

Checksum running on receiving packets are the most significant cost of
CPU time in local-tun.
---
 crates/shadowsocks-service/Cargo.toml               |  1 +
 crates/shadowsocks-service/src/local/tun/tcp.rs     | 13 +++++++++----
 .../src/local/tun/virt_device.rs                    |  1 +
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/crates/shadowsocks-service/Cargo.toml b/crates/shadowsocks-service/Cargo.toml
index 9c14bad6..53188a91 100644
--- a/crates/shadowsocks-service/Cargo.toml
+++ b/crates/shadowsocks-service/Cargo.toml
@@ -185,6 +185,7 @@ smoltcp = { version = "0.12", optional = true, default-features = false, feature
     "log",
     "medium-ip",
     "proto-ipv4",
+    "proto-ipv4-fragmentation",
     "proto-ipv6",
     "socket-icmp",
     "socket-udp",
diff --git a/crates/shadowsocks-service/src/local/tun/tcp.rs b/crates/shadowsocks-service/src/local/tun/tcp.rs
index 3096c4f5..42889bfe 100644
--- a/crates/shadowsocks-service/src/local/tun/tcp.rs
+++ b/crates/shadowsocks-service/src/local/tun/tcp.rs
@@ -18,7 +18,7 @@ use log::{debug, error, trace};
 use shadowsocks::{net::TcpSocketOpts, relay::socks5::Address};
 use smoltcp::{
     iface::{Config as InterfaceConfig, Interface, PollResult, SocketHandle, SocketSet},
-    phy::{DeviceCapabilities, Medium},
+    phy::{Checksum, DeviceCapabilities, Medium},
     socket::tcp::{CongestionControl, Socket as TcpSocket, SocketBuffer as TcpSocketBuffer, State as TcpState},
     storage::RingBuffer,
     time::{Duration as SmolDuration, Instant as SmolInstant},
@@ -42,9 +42,9 @@ use crate::{
 
 use super::virt_device::VirtTunDevice;
 
-// NOTE: Default buffer could contain 20 AEAD packets
-const DEFAULT_TCP_SEND_BUFFER_SIZE: u32 = 0x3FFF * 20;
-const DEFAULT_TCP_RECV_BUFFER_SIZE: u32 = 0x3FFF * 20;
+// NOTE: Default buffer could contain 5 AEAD packets
+const DEFAULT_TCP_SEND_BUFFER_SIZE: u32 = (0x3FFFu32 * 5).next_power_of_two();
+const DEFAULT_TCP_RECV_BUFFER_SIZE: u32 = (0x3FFFu32 * 5).next_power_of_two();
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
 enum TcpSocketState {
@@ -261,6 +261,11 @@ impl TcpTun {
         let mut capabilities = DeviceCapabilities::default();
         capabilities.medium = Medium::Ip;
         capabilities.max_transmission_unit = mtu as usize;
+        capabilities.checksum.ipv4 = Checksum::Tx;
+        capabilities.checksum.tcp = Checksum::Tx;
+        capabilities.checksum.udp = Checksum::Tx;
+        capabilities.checksum.icmpv4 = Checksum::Tx;
+        capabilities.checksum.icmpv6 = Checksum::Tx;
 
         let (mut device, iface_rx, iface_tx, iface_tx_avail) = VirtTunDevice::new(capabilities);
 
diff --git a/crates/shadowsocks-service/src/local/tun/virt_device.rs b/crates/shadowsocks-service/src/local/tun/virt_device.rs
index 6fdc797d..1dc06fc8 100644
--- a/crates/shadowsocks-service/src/local/tun/virt_device.rs
+++ b/crates/shadowsocks-service/src/local/tun/virt_device.rs
@@ -64,6 +64,7 @@ impl Device for VirtTunDevice {
                 buffer,
                 phantom_device: PhantomData,
             };
+            self.in_buf_avail.store(true, Ordering::Release);
             let tx = VirtTxToken(self);
             return Some((rx, tx));
         }