tor-browser

commit 5a9502cb10e897146a993dd18d7a02ba4cdae295
parent 7f3efcc6563cab0c86447b9405548ddaaee2f294
Author: Oskar Mansfeld <git@omansfeld.net>
Date:   Mon,  8 Dec 2025 16:33:23 +0000

Bug 1992148 - Add metric to track spurious congestion event ratio. r=mxinden,necko-reviewers,kershaw

Tracks the ratio of spurious congestion events to loss induced
congestion events. Uses a scaling factor of 10k.

I gave the probe a range_max of 10k (which would represent every
congestion event being spurious), because while I expect the overall
ratio to be much lower, it is most likely that a connection seeing some
spurious congestion will see a lot of it, while other connections see
none at all. So setting the range_max to something lower might cut those
single data points off. It's the same reason why this is a linear
histogram and not an exponential one.

Differential Revision: https://phabricator.services.mozilla.com/D275053

Diffstat:
M
netwerk/metrics.yaml
 | 
20
++++++++++++++++++++
M
netwerk/socket/neqo_glue/src/lib.rs
 | 
15
+++++++++++++++

2 files changed, 35 insertions(+), 0 deletions(-)
diff --git a/netwerk/metrics.yaml b/netwerk/metrics.yaml
@@ -1094,6 +1094,26 @@ networking:
       - minden@mozilla.com
     expires: never
 
+  http_3_spurious_congestion_event_ratio:
+    type: custom_distribution
+    unit: integer
+    range_min: 0
+    range_max: 10000
+    bucket_count: 100
+    histogram_type: linear
+    description: >
+      HTTP3: spurious congestion event to loss induced congestion event ratio (10000 scaling factor).
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1992148
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1992148
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - necko@mozilla.com
+      - omansfeld@mozilla.com
+    expires: 157
+
   http_3_connection_close_reason:
     type: labeled_counter
     description: >
diff --git a/netwerk/socket/neqo_glue/src/lib.rs b/netwerk/socket/neqo_glue/src/lib.rs
@@ -684,6 +684,21 @@ impl NeqoHttp3Conn {
                 debug_assert!(false, "{msg}");
             }
         }
+
+        // Ignore connections that never had loss induced congestion events (and prevent dividing by zero)
+        if stats.cc.congestion_events_loss != 0 {
+            if let Ok(spurious) = i64::try_from(
+                (stats.cc.congestion_events_spurious * PRECISION_FACTOR_USIZE)
+                    / stats.cc.congestion_events_loss,
+            ) {
+                glean::http_3_spurious_congestion_event_ratio
+                    .accumulate_single_sample_signed(spurious);
+            } else {
+                let msg = "Failed to convert ratio to i64 for use with glean";
+                qwarn!("{msg}");
+                debug_assert!(false, "{msg}");
+            }
+        }
     }
 
     fn increment_would_block_rx(&mut self) {