feat: use Cubic CC by default (#2295)

* feat: use Cubic CC by default

Firefox uses Cubic by default:

``` yaml
- name: network.http.http3.cc_algorithm
  type: RelaxedAtomicUint32
  value: 1
  mirror: always
  rust: true
```

https://searchfox.org/mozilla-central/rev/f9517009d8a4946dbdd3acd72a31dc34fca79586/modules/libpref/init/StaticPrefList.yaml

This commit updates Neqo to use Cubic instead of New Reno by default.

* test(cc): support both cubic and new reno

* Trigger CI

neqo-bin/src/lib.rs

@@ -112,7 +112,7 @@ pub struct QuicParameters {
     /// The idle timeout for connections, in seconds.
     pub idle_timeout: u64,
 
-    #[arg(long = "cc", default_value = "newreno")]
+    #[arg(long = "cc", default_value = "cubic")]
     /// The congestion controller to use.
     pub congestion_control: CongestionControlAlgorithm,
 
@@ -145,7 +145,7 @@ impl Default for QuicParameters {
             max_streams_bidi: 16,
             max_streams_uni: 16,
             idle_timeout: 30,
-            congestion_control: CongestionControlAlgorithm::NewReno,
+            congestion_control: CongestionControlAlgorithm::Cubic,
             no_pacing: false,
             no_pmtud: false,
             preferred_address_v4: None,

neqo-transport/src/cc/tests/cubic.rs

@@ -180,7 +180,7 @@ fn tcp_phase() {
     assert!(num_acks2 < expected_ack_tcp_increase2);
 
     // The time needed to increase cwnd by MAX_DATAGRAM_SIZE using the cubic equation will be
-    // calculates from: W_cubic(elapsed_time + t_to_increase) - W_cubic(elapsed_time) =
+    // calculated from: W_cubic(elapsed_time + t_to_increase) - W_cubic(elapsed_time) =
     // MAX_DATAGRAM_SIZE => CUBIC_C * (elapsed_time + t_to_increase)^3 * MAX_DATAGRAM_SIZE +
     // CWND_INITIAL - CUBIC_C * elapsed_time^3 * MAX_DATAGRAM_SIZE + CWND_INITIAL =
     // MAX_DATAGRAM_SIZE => t_to_increase = cbrt((1 + CUBIC_C * elapsed_time^3) / CUBIC_C) -

neqo-transport/src/connection/params.rs

@@ -91,7 +91,7 @@ impl Default for ConnectionParameters {
     fn default() -> Self {
         Self {
             versions: VersionConfig::default(),
-            cc_algorithm: CongestionControlAlgorithm::NewReno,
+            cc_algorithm: CongestionControlAlgorithm::Cubic,
             max_data: LOCAL_MAX_DATA,
             max_stream_data_bidi_remote: u64::try_from(RECV_BUFFER_SIZE).unwrap(),
             max_stream_data_bidi_local: u64::try_from(RECV_BUFFER_SIZE).unwrap(),

neqo-transport/src/connection/tests/cc.rs

@@ -19,8 +19,7 @@ use crate::{
     recovery::{ACK_ONLY_SIZE_LIMIT, PACKET_THRESHOLD},
     sender::PACING_BURST_SIZE,
     stream_id::StreamType,
-    tracking::DEFAULT_ACK_PACKET_TOLERANCE,
-    ConnectionParameters,
+    CongestionControlAlgorithm, ConnectionParameters,
 };
 
 #[test]
@@ -211,12 +210,11 @@ fn single_packet_on_recovery() {
     assert!(dgram.is_some());
 }
 
-#[test]
 /// Verify that CC moves out of recovery period when packet sent after start
 /// of recovery period is acked.
-fn cc_cong_avoidance_recovery_period_to_cong_avoidance() {
-    let mut client = default_client();
-    let mut server = default_server();
+fn cc_cong_avoidance_recovery_period_to_cong_avoidance(cc_algorithm: CongestionControlAlgorithm) {
+    let mut client = new_client(ConnectionParameters::default().cc_algorithm(cc_algorithm));
+    let mut server = new_server(ConnectionParameters::default().cc_algorithm(cc_algorithm));
     let now = connect_rtt_idle(&mut client, &mut server, DEFAULT_RTT);
 
     // Create stream 0
@@ -233,59 +231,45 @@ fn cc_cong_avoidance_recovery_period_to_cong_avoidance() {
     now += DEFAULT_RTT / 2;
     let s_ack = ack_bytes(&mut server, stream_id, c_tx_dgrams, now);
 
+    let cwnd_before_loss = cwnd(&client);
+
     // Client: Process ack
     now += DEFAULT_RTT / 2;
     client.process_input(s_ack, now);
 
+    let cwnd_after_loss = cwnd(&client);
+
     // Should be in CARP now.
     now += DEFAULT_RTT / 2;
+    assert!(cwnd_before_loss > cwnd_after_loss);
     qinfo!("moving to congestion avoidance {}", cwnd(&client));
 
-    // Now make sure that we increase congestion window according to the
-    // accurate byte counting version of congestion avoidance.
-    // Check over several increases to be sure.
-    let mut expected_cwnd = cwnd(&client);
-    // Fill cwnd.
-    let (mut c_tx_dgrams, next_now) = fill_cwnd(&mut client, stream_id, now);
-    now = next_now;
-    for i in 0..5 {
+    for i in 0..6 {
         qinfo!("iteration {i}");
 
-        let c_tx_size: usize = c_tx_dgrams.iter().map(Datagram::len).sum();
+        let (c_tx_dgrams, next_now) = fill_cwnd(&mut client, stream_id, now);
         qinfo!(
-            "client sending {c_tx_size} bytes into cwnd of {}",
+            "client sending {} bytes into cwnd of {}",
+            c_tx_dgrams.iter().map(Datagram::len).sum::<usize>(),
             cwnd(&client)
         );
-        assert_eq!(c_tx_size, expected_cwnd);
-
-        // As acks arrive we will continue filling cwnd and save all packets
-        // from this cycle will be stored in next_c_tx_dgrams.
-        let mut next_c_tx_dgrams: Vec<Datagram> = Vec::new();
-
-        // Until we process all the packets, the congestion window remains the same.
-        // Note that we need the client to process ACK frames in stages, so split the
-        // datagrams into two, ensuring that we allow for an ACK for each batch.
-        let most = c_tx_dgrams.len() - usize::try_from(DEFAULT_ACK_PACKET_TOLERANCE).unwrap() - 1;
-        let s_ack = ack_bytes(&mut server, stream_id, c_tx_dgrams.drain(..most), now);
-        assert_eq!(cwnd(&client), expected_cwnd);
-        client.process_input(s_ack, now);
-        // make sure to fill cwnd again.
-        let (mut new_pkts, next_now) = fill_cwnd(&mut client, stream_id, now);
         now = next_now;
-        next_c_tx_dgrams.append(&mut new_pkts);
 
         let s_ack = ack_bytes(&mut server, stream_id, c_tx_dgrams, now);
-        assert_eq!(cwnd(&client), expected_cwnd);
         client.process_input(s_ack, now);
-        // make sure to fill cwnd again.
-        let (mut new_pkts, next_now) = fill_cwnd(&mut client, stream_id, now);
-        now = next_now;
-        next_c_tx_dgrams.append(&mut new_pkts);
-
-        expected_cwnd += client.plpmtu();
-        assert_eq!(cwnd(&client), expected_cwnd);
-        c_tx_dgrams = next_c_tx_dgrams;
     }
+
+    assert!(cwnd_before_loss < cwnd(&client));
+}
+
+#[test]
+fn cc_cong_avoidance_recovery_period_to_cong_avoidance_new_reno() {
+    cc_cong_avoidance_recovery_period_to_cong_avoidance(CongestionControlAlgorithm::NewReno);
+}
+
+#[test]
+fn cc_cong_avoidance_recovery_period_to_cong_avoidance_cubic() {
+    cc_cong_avoidance_recovery_period_to_cong_avoidance(CongestionControlAlgorithm::Cubic);
 }
 
 #[test]