Bug 1814718 - Added telemetry for number of timers fired per Timer Thread wake-up. r=smaug,florian

Differential Revision: https://phabricator.services.mozilla.com/D168915

toolkit/components/glean/metrics_index.py

@@ -26,6 +26,7 @@ gecko_metrics = [
     "toolkit/components/glean/metrics.yaml",
     "toolkit/components/pdfjs/metrics.yaml",
     "toolkit/components/processtools/metrics.yaml",
+    "xpcom/metrics.yaml",
 ]
 
 # Metrics that are sent by Firefox Desktop

xpcom/metrics.yaml

@@ -0,0 +1,30 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Adding a new metric? We have docs for that!
+# https://firefox-source-docs.mozilla.org/toolkit/components/glean/user/new_definitions_file.html
+
+---
+$schema: moz://mozilla.org/schemas/glean/metrics/2-0-0
+$tags:
+  - "Core :: XPCOM"
+
+timer_thread:
+  timers_fired_per_wakeup:
+    type: custom_distribution
+    description: >
+      How many timers were processed in a single wake-up of the Timer Thread.
+    range_min: 0
+    range_max: 80
+    bucket_count: 20
+    histogram_type: exponential
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1814718
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1814718
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - jlink@mozilla.com
+    expires: never

xpcom/threads/TimerThread.cpp

@@ -20,6 +20,8 @@
 #include "mozilla/OperatorNewExtensions.h"
 #include "mozilla/StaticPrefs_timer.h"
 
+#include "mozilla/glean/GleanMetrics.h"
+
 #include <math.h>
 
 using namespace mozilla;
@@ -539,6 +541,7 @@ TimerThread::Run() {
   mAllowedEarlyFiringMicroseconds = usIntervalResolution / 2;
   bool forceRunNextTimer = false;
 
+  uint64_t timersFiredThisWakeup = 0;
   while (!mShutdown) {
     // Have to use PRIntervalTime here, since PR_WaitCondVar takes it
     TimeDuration waitFor;
@@ -581,6 +584,7 @@ TimerThread::Run() {
           // release of the timer so that we don't end up releasing the timer
           // on the TimerThread instead of on the thread it targets.
           {
+            ++timersFiredThisWakeup;
             LogTimerEvent::Run run(timerRef.get());
             PostTimerEvent(timerRef.forget());
           }
@@ -643,6 +647,10 @@ TimerThread::Run() {
     mWaiting = true;
     mNotified = false;
     {
+      // About to sleep - let's make note of how many timers we processed.
+      glean::timer_thread::timers_fired_per_wakeup.AccumulateSamples(
+          {timersFiredThisWakeup});
+      timersFiredThisWakeup = 0;
       AUTO_PROFILER_TRACING_MARKER("TimerThread", "Wait", OTHER);
       mMonitor.Wait(waitFor);
     }