f redo max tick interval logic, this much better matches reality

Author: TheBlueMatt

lightning/src/ln/peer_handler.rs

@@ -298,23 +298,27 @@ const OUTBOUND_BUFFER_LIMIT_READ_PAUSE: usize = 10;
 /// the peer.
 const OUTBOUND_BUFFER_LIMIT_DROP_GOSSIP: usize = OUTBOUND_BUFFER_LIMIT_READ_PAUSE * FORWARD_INIT_SYNC_BUFFER_SIZE_LIMIT;
 
-/// If we've sent a ping, and are still awaiting a response, we (or our peer) may need to churn our
-/// (or their) way through the socket receive buffer before receiving the ping.
+/// If we've sent a ping, and are still awaiting a response, we may need to churn our way through
+/// the socket receive buffer before receiving the ping.
 ///
 /// On a fairly old Arm64 board, with Linux defaults, this can take as long as 20 seconds, not
-/// including any network delays or outbound traffic.
+/// including any network delays, outbound traffic, or the same for messages from other peers.
 ///
 /// Thus, to avoid needlessly disconnecting a peer, we allow a peer to take this many timer ticks
-/// to respond to a ping, as long as they send us at least one message during each tick or if we
-/// sent a lot of messages, ensuring we aren't actually just disconnected. With a timer tick
-/// interval of five seconds, this translates to about 30 seconds.
-pub const MAX_BUFFER_DRAIN_TICK_INTERVALS: i8 = 6;
+/// per connected peer to respond to a ping, as long as they send us at least one message during
+/// each tick, ensuring we aren't actually just disconnected.
+/// With a timer tick interval of five seconds, this translates to about 30 seconds per connected
+/// peer.
+///
+/// When we improve parallelism somewhat we should reduce this to e.g. this many timer ticks per
+/// two connected peers, assuming most LDK-running systems have at least two cores.
+const MAX_BUFFER_DRAIN_TICK_INTERVALS_PER_PEER: i8 = 6;
 
 /// This is the minimum number of messages we expect a peer to be able to handle within one timer
 /// tick. Once we have sent this many messages since the last ping, we send a ping right away to
 /// ensures we don't just fill up our send buffer and leave the peer with too many messages to
 /// process before the next ping.
-pub const BUFFER_DRAIN_MSGS_PER_TICK: usize = 32;
+const BUFFER_DRAIN_MSGS_PER_TICK: usize = 32;
 
 struct Peer {
 	channel_encryptor: PeerChannelEncryptor,
@@ -1523,6 +1527,7 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, L: Deref, CMH: Deref> P
 			let node_id_to_descriptor = &mut peers.node_id_to_descriptor;
 			let peers = &mut peers.peers;
 			let mut descriptors_needing_disconnect = Vec::new();
+			let peer_count = peers.len();
 
 			peers.retain(|descriptor, peer| {
 				if !peer.channel_encryptor.is_ready_for_encryption() {
@@ -1531,7 +1536,8 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, L: Deref, CMH: Deref> P
 				}
 
 				if (peer.awaiting_pong_tick_intervals > 0 && !peer.received_message_since_timer_tick)
-					|| peer.awaiting_pong_tick_intervals > MAX_BUFFER_DRAIN_TICK_INTERVALS
+					|| peer.awaiting_pong_tick_intervals as u64 >
+						MAX_BUFFER_DRAIN_TICK_INTERVALS_PER_PEER as u64 * peer_count as u64
 				{
 					descriptors_needing_disconnect.push(descriptor.clone());
 					match peer.their_node_id {