dtourolle/KPN
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

fix: NodeSnapshot fields must line up with what nodes supply

Browse Source 
a8cfe73 appended queued/wake_pending/total_exec_ms to the NodeSnapshot
aggregate in an order no call site used. Every node type fills the aggregate
positionally and all of them supply total_exec_ms as the element straight
after queue_wait_ms — but the struct declared the two bools there. So the
exec total landed in `queued`, `queued` landed in `wake_pending`, and
`wake_pending` landed in total_exec_ms.

GCC reported it as -Wnarrowing (bool to double), 88 times, once per node
instantiation across the test build. The build carried on.

This is worse than a cosmetic mix-up, because all three fields were added
specifically to diagnose a wedge. A wedged pipeline reported total_exec_ms
as 0.0 or 1.0, and `queued` as "has this node ever run" — true for every
node that had, including ones asleep with nothing to do. The web debug JSON
served the same values. Anyone reading them to find the stalled node would
have been pointed at the wrong one.

Moves total_exec_ms above the two bools to match every call site, and notes
in the struct why the order is load-bearing.

Verified in both directions: on a8cfe73 the new case reports frames=8
total=0 queued=true; here total >= ema and both flags are false.
This commit is contained in:
dtourolle
2026-08-05 12:46:56 +02:00
parent a8cfe7300a
commit 091211cb19
2 changed files with 56 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/kpn/diagnostics.hpp
+10 -5
View File
@@ -157,6 +157,16 @@ struct NodeSnapshot {
double cpu_util_pct; // exec_ms / (exec_ms + blocked_ms) * 100
double queue_wait_ms{0}; // PoolNode: cumulative time spent in pool queue
// Cumulative wall time inside fire_once. Unlike ema_exec_ms this is a true
// sum, so it is the field to use for "share of the run spent in this node".
// Note it still includes time parked pushing into a full output channel;
// total_cpu_ms is the part that backpressure cannot inflate.
//
// Declared before the two bools below because every node type initialises
// this aggregate positionally, and all of them supply total_exec_ms as the
// element after queue_wait_ms.
double total_exec_ms{0};
// Live scheduling state, for observing the AR-004 invariant "a node never
// sleeps with a wake outstanding". The invariant was previously asserted in
// comments but invisible at runtime, so a lost wake could only be found in a
@@ -169,11 +179,6 @@ struct NodeSnapshot {
// queued=1 while nothing running -> submitted but never scheduled
bool queued{false};
bool wake_pending{false};
// Cumulative wall time inside fire_once. Unlike ema_exec_ms this is a true
// sum, so it is the field to use for "share of the run spent in this node".
// Note it still includes time parked pushing into a full output channel;
// total_cpu_ms is the part that backpressure cannot inflate.
double total_exec_ms{0};
};
// ── Pool statistics + snapshot ────────────────────────────────────────────────