Bug 1538987 - Collect Telemetry on process priority switching. data-r…

…eview=chutten, r=gsvelto

Differential Revision: https://phabricator.services.mozilla.com/D25137

--HG--
extra : moz-landing-system : lando

dom/ipc/ProcessPriorityManager.cpp

@@ -13,6 +13,7 @@
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/Services.h"
+#include "mozilla/Telemetry.h"
 #include "mozilla/Unused.h"
 #include "mozilla/Logging.h"
 #include "nsPrintfCString.h"
@@ -493,6 +494,9 @@ void ProcessPriorityManagerImpl::TabActivityChanged(TabParent* aTabParent,
     return;
   }
 
+  Telemetry::ScalarAdd(
+      Telemetry::ScalarID::DOM_CONTENTPROCESS_OS_PRIORITY_CHANGE_CONSIDERED, 1);
+
   pppm->TabActivityChanged(aTabParent, aIsActive);
 }
 
@@ -795,6 +799,15 @@ void ParticularProcessPriorityManager::SetPriorityNow(
   ProcessPriority oldPriority = mPriority;
 
   mPriority = aPriority;
+
+  if (oldPriority < mPriority) {
+    Telemetry::ScalarAdd(
+        Telemetry::ScalarID::DOM_CONTENTPROCESS_OS_PRIORITY_RAISED, 1);
+  } else {
+    Telemetry::ScalarAdd(
+        Telemetry::ScalarID::DOM_CONTENTPROCESS_OS_PRIORITY_LOWERED, 1);
+  }
+
   hal::SetProcessPriority(Pid(), mPriority);
 
   if (oldPriority != mPriority) {

toolkit/components/telemetry/Scalars.yaml

@@ -1085,6 +1085,49 @@ dom.contentprocess:
     release_channel_collection: opt-out
     record_in_processes:
       - 'main'
+  os_priority_lowered:
+    bug_numbers:
+      - 1538987
+    description: >
+      The number of times a content process has had its OS priority lowered
+      due to only containing background tabs without audible media playing.
+    expires: never
+    kind: uint
+    notification_emails:
+      - [email protected]
+      - [email protected]
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
+  os_priority_raised:
+    bug_numbers:
+      - 1538987
+    description: >
+      The number of times a content process has had its OS priority raised
+      due to containing at least one foregrounded tab, or a tab with audible
+      media has started playing in it.
+    expires: never
+    kind: uint
+    notification_emails:
+      - [email protected]
+      - [email protected]
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
+  os_priority_change_considered:
+    bug_numbers:
+      - 1538987
+    description: >
+      The number of times we've had the opportunity to change content process
+      priority due to a tab switch or a tab being opened.
+    expires: never
+    kind: uint
+    notification_emails:
+      - [email protected]
+      - [email protected]
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
 
 # The following section contains parent process base counters.
 dom.parentprocess: