Bug 1957331 - QM: Add telemetry for shutdown time excluding suspend; r=dom-storage-reviewers,jstutte

This patch adds a new Glean timing_distribution metric, to measure the duration
of QuotaManager shutdown.

The measurement runs on the PBackground thread and uses NowExcludingSuspendMs
to exclude any system suspend time (e.g. sleep or hibernation), providing a
more accurate view of active runtime cost.

This helps monitor shutdown performance and detect improvements or regressions,
especially for users with significant storage data.

Telemetry metadata was added under dom/quota/metrics.yaml.

Differential Revision: https://phabricator.services.mozilla.com/D243625

dom/quota/ActorsParent.cpp

@@ -1840,8 +1840,32 @@ void QuotaManager::ShutdownInstance() {
 
     recordTimeDeltaHelper->Start();
 
+    // Glean SDK recommends using its own timing APIs where possible. In this
+    // case, we use NowExcludingSuspendMs() directly to manually calculate a
+    // duration that excludes suspend time. This is a valid exception because
+    // our use case is sensitive to suspend, and we need full control over the
+    // timing logic.
+    //
+    // We are currently recording both this and the older helper-based
+    // measurement. The results are not directly comparable, since the new API
+    // uses monotonic time. If this approach proves more reliable, we'll retire
+    // the old telemetry, change the expiration of the new metric to never,
+    // and add a matching "including suspend" version.
+
+    const auto startExcludingSuspendMs = NowExcludingSuspendMs();
+
     gInstance->Shutdown();
 
+    const auto endExcludingSuspendMs = NowExcludingSuspendMs();
+
+    if (startExcludingSuspendMs && endExcludingSuspendMs) {
+      const auto duration = TimeDuration::FromMilliseconds(
+          *endExcludingSuspendMs - *startExcludingSuspendMs);
+
+      glean::quotamanager_shutdown::total_time_excluding_suspend
+          .AccumulateRawDuration(duration);
+    }
+
     recordTimeDeltaHelper->End();
 
     gInstance = nullptr;

dom/quota/metrics.yaml

@@ -129,6 +129,34 @@ quotamanager.initialize.temporarystorage:
       - jvarga@mozilla.com
       - storage-telemetry@mozilla.com
     expires: 141
+quotamanager.shutdown:
+  total_time_excluding_suspend:
+    type: timing_distribution
+    time_unit: millisecond
+    description: >
+      This metric logs the total time required to shut down the QuotaManager
+      instance on the PBackground thread. The duration excludes any periods
+      when the system was suspended (system sleep or hibernation), to better
+      reflect actual time spent performing shutdown.
+      While the shutdown process is measured on the PBackground thread, it
+      involves spinning the event loop and thus waiting for operations on other
+      threads (especially I/O threads) to complete.
+      The primary goal is to measure the actual runtime cost of shutdown under
+      typical conditions, without distortion from system-level suspension
+      delays.
+      This data can help detect performance regressions or improvements related
+      to QuotaManager shutdown behavior, especially in scenarios involving
+      large amounts of user storage data.
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1590635
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1590635
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - jvarga@mozilla.com
+      - storage-telemetry@mozilla.com
+    expires: 141
 
 dom.quota:
   info_load_time: