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Test cost-based parent selection and kernel-drop detection as unit tests

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The cost-selection chaos scenarios (cost-reeval, cost-avoidance,
cost-stability, depth-vs-cost, mixed-technology, bottleneck-parent) tested
TreeState::evaluate_parent's decision logic through a Docker mesh that could
not exercise it reliably: the tree roots at whichever node holds the smallest
NodeAddr, MMP link costs take several measurement windows to settle, and the
parent hold-down plus hysteresis timing all confound the outcome. A
deterministic link-cost flap still produced zero periodic parent switches in a
full run.

Replace those six scenarios with deterministic unit tests in src/tree/tests.rs
that drive evaluate_parent directly: cheaper-link selection at equal depth,
switch-on-cost-change, hysteresis suppressing a marginal change while allowing
a significant one, and the depth-versus-cost effective-depth tradeoff. Each is
constructed so that breaking the cost or hysteresis logic makes it fail.

The congestion kernel-drop signal (SO_RXQ_OVFL) cannot be provoked
deterministically in Docker: a fresh daemon reader keeps up with
container-speed traffic, so the socket receive queue never overflows (an
unshaped run with a 4 KB buffer and heavy traffic recorded zero drops on every
node). Extract the drop-detection edge -- read the cumulative counter, fire an
event only on the transition into a new drop burst -- into
TransportDropState::observe_drops and unit-test it directly. congestion-stress
keeps its ECN and MMP congestion-signal assertions, which do need the real
shaped bottleneck queue.

Remove the retired scenarios from both CI runners and update the chaos README.
This commit is contained in:
Johnathan Corgan
2026-07-23 23:33:01 +00:00
parent be5deee814
commit 08a226fb63
16 changed files with 299 additions and 824 deletions
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src/node/handlers/forwarding.rs
+4 -7
View File
@@ -417,13 +417,10 @@ impl Node {
for (&tid, transport) in &self.transports {
let congestion = transport.congestion();
let state = self.transport_drops.entry(tid).or_default();
if let Some(current) = congestion.recv_drops {
let new_drops = current > state.prev_drops;
if new_drops && !state.dropping {
new_drop_events.push(tid);
}
state.dropping = new_drops;
state.prev_drops = current;
if let Some(current) = congestion.recv_drops
&& state.observe_drops(current)
{
new_drop_events.push(tid);
}
}
for tid in new_drop_events {