Add jitter

src/net/xdp.rs

@@ -356,6 +356,8 @@ pub fn spawn(workers: XdpWorkers, config: Arc<crate::Config>) -> Result<XdpLoop,
 const BATCH_SIZE: usize = 64;
 use xdp::packet::net_types::NetworkU16;
 
+use crate::time::UtcTimestamp;
+
 /// The core I/O loop
 ///
 /// All of the ring operations are done in this loop so that the actual
@@ -393,6 +395,7 @@ fn io_loop(
         sessions,
         local_ipv4,
         local_ipv6,
+        last_receive: UtcTimestamp::now(),
     };
 
     let mut rx_slab = xdp::HeapSlab::with_capacity(BATCH_SIZE);

src/net/xdp/process.rs

@@ -6,6 +6,7 @@ use crate::{
         maxmind_db::{self, IpNetEntry},
         EndpointAddress,
     },
+    time::UtcTimestamp,
 };
 pub use quilkin_xdp::xdp;
 use quilkin_xdp::xdp::{
@@ -114,6 +115,7 @@ pub struct State {
     pub sessions: Arc<SessionState>,
     pub local_ipv4: std::net::Ipv4Addr,
     pub local_ipv6: std::net::Ipv6Addr,
+    pub last_receive: UtcTimestamp,
 }
 
 impl State {
@@ -440,6 +442,11 @@ pub fn process_packets(
     let filters = state.config.filters.load();
     let cm = state.config.clusters.clone_value();
 
+    let now = UtcTimestamp::now();
+    let jitter = (now - state.last_receive).nanos();
+    state.last_receive = now;
+    let mut had_read = false;
+
     while let Some(inner) = rx_slab.pop_front() {
         let Ok(Some(udp)) = UdpPacket::parse_packet(&inner) else {
             unreachable!("we somehow got a non-UDP packet, this should be impossible with the eBPF program we use to route packets");
@@ -452,6 +459,7 @@ pub fn process_packets(
 
         let is_client = udp.dst_port == state.external_port;
         let direction = if is_client {
+            had_read = true;
             metrics::READ
         } else {
             metrics::WRITE
@@ -465,7 +473,7 @@ pub fn process_packets(
             if is_client {
                 process_client_packet(packet, umem, &filters, &cm, state, tx_slab)
             } else {
-                process_server_packet(packet, umem, &filters, state, tx_slab)
+                process_server_packet(packet, umem, &filters, state, tx_slab, jitter)
             }
         };
 
@@ -483,6 +491,10 @@ pub fn process_packets(
             }
         }
     }
+
+    if had_read {
+        metrics::packet_jitter(metrics::READ, &metrics::EMPTY).set(jitter);
+    }
 }
 
 #[inline]
@@ -630,6 +642,7 @@ fn process_server_packet(
     filters: &crate::filters::FilterChain,
     state: &mut State,
     tx_slab: &mut HeapSlab,
+    jitter: i64,
 ) -> Result<Option<Packet>, (PipelineError, Packet)> {
     let server_addr = SocketAddr::new(packet.udp.ips.source(), packet.udp.src_port.host());
 
@@ -638,6 +651,8 @@ fn process_server_packet(
         return Ok(Some(packet.inner));
     };
 
+    metrics::packet_jitter(metrics::Direction::Write, &asn).set(jitter);
+
     let mut ctx = filters::WriteContext::new(server_addr.into(), client_addr.into(), packet);
 
     let mut packet = match filters.write(&mut ctx) {