From 87b7133c9db82c4db4238908481a2a848d171010 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Wed, 4 Nov 2026 23:48:02 +0100
Subject: benchmark bridge slow link

---
 src/simtest/bench.rs | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

(limited to 'src')

diff --git a/src/simtest/bench.rs b/src/simtest/bench.rs
index 426507b..ab1809d 100644
--- a/src/simtest/bench.rs
+++ b/src/simtest/bench.rs
@@ -664,9 +664,13 @@ const BRIDGE_WRITES: usize = 200;
 const BRIDGE_VALUE: usize = 256 * 1024;
 /// A hundred a second.
 const BRIDGE_EVERY: Duration = Duration::from_millis(10);
+/// The slow transport, unless `BENCH_BRIDGE_SLOW_RATE` (MiB/s) and
+/// `BENCH_BRIDGE_SLOW_RTT` (ms) say otherwise.
+const BRIDGE_SLOW_RATE_MIB: u64 = 50;
+const BRIDGE_SLOW_RTT_MS: u64 = 500;
 
 /// A writer on a fast transport (5 ms round trips, 1 GiB/s), a bridge on it and a slow
-/// one (500 ms round trips, 50 MiB/s), and a node on the slow one alone: a writes 256
+/// one (500 ms round trips, 50 MiB/s, by default), and a node on the slow one alone: a writes 256
 /// KiB values at 100 a second (25 MiB/s, a quarter of the fast link, half of the slow
 /// one), b passes them on to z. What z gets, as sync messages and as blobs (deltas),
 /// against what was written, and how late.
@@ -674,19 +678,26 @@ const BRIDGE_EVERY: Duration = Duration::from_millis(10);
 #[ignore = "a benchmark: cargo benchmarks"]
 async fn bench_bridge() {
     println!();
-    let writes = std::env::var("BENCH_BRIDGE_WRITES")
-        .ok()
-        .and_then(|writes| writes.parse().ok())
-        .unwrap_or(BRIDGE_WRITES);
+    let env = |name: &str, default| {
+        std::env::var(name)
+            .ok()
+            .and_then(|value| value.parse().ok())
+            .unwrap_or(default)
+    };
+    let writes = env("BENCH_BRIDGE_WRITES", BRIDGE_WRITES as u64) as usize;
+    let slow_rate = env("BENCH_BRIDGE_SLOW_RATE", BRIDGE_SLOW_RATE_MIB);
+    let slow_rtt = env("BENCH_BRIDGE_SLOW_RTT", BRIDGE_SLOW_RTT_MS);
     let sim = Sim::with_identity(71);
     sim.net.set_default_link(LinkParams {
         delay: (Duration::from_micros(2_000), Duration::from_micros(3_000)),
         rate: Some(1 << 30),
         ..LinkParams::default()
     });
+    // Half the round trip each way, give or take a twentieth.
+    let half = Duration::from_millis(slow_rtt / 2);
     sim.net_for("sim2").set_default_link(LinkParams {
-        delay: (Duration::from_millis(240), Duration::from_millis(260)),
-        rate: Some(50 << 20),
+        delay: (half - half / 20, half + half / 20),
+        rate: Some(slow_rate << 20),
         ..LinkParams::default()
     });
     let timing = |config: &mut crate::node::NodeConfig| {
@@ -752,7 +763,7 @@ async fn bench_bridge() {
             .map_or("beyond the last bucket".to_owned(), |ms| format!("{ms} ms"))
     };
     println!(
-        "\nfast writer, bridge, slow node ({writes} values of {} KiB, {} a second)\n  \
+        "\nfast writer, bridge, slow node ({writes} values of {} KiB, {} a second; slow link {slow_rate} MiB/s, {slow_rtt} ms round trips)\n  \
          written: {:.1} MiB in {:.1} s; z converged {} ms after the last write\n  \
          b sent (to a and z): SYNC {} messages, {:.1} MiB; BLOB {} messages, {:.1} MiB\n  \
          z received: SYNC {} messages, {:.1} MiB; BLOB {} messages, {:.1} MiB: {:.2} times what was written\n  \
-- 
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