Bug 758206 - Telemetry for preload/prefetch. r=taras

browser/app/nsBrowserApp.cpp

@@ -214,6 +214,12 @@ int main(int argc, char* argv[])
   struct rusage initialRUsage;
   gotCounters = !getrusage(RUSAGE_SELF, &initialRUsage);
 #elif defined(XP_WIN)
+  // Don't change the order of these enumeration constants, the order matters
+  // for reporting telemetry data.  If new values are added adjust the
+  // STARTUP_USING_PRELOAD histogram.
+  enum PreloadReason { PRELOAD_NONE, PRELOAD_SERVICE, PRELOAD_IOCOUNT };
+  PreloadReason preloadReason = PRELOAD_NONE;
+
   // GetProcessIoCounters().ReadOperationCount seems to have little to
   // do with actual read operations. It reports 0 or 1 at this stage
   // in the program. Luckily 1 coincides with when prefetch is
@@ -224,14 +230,19 @@ int main(int argc, char* argv[])
   // files.
   IO_COUNTERS ioCounters;
   gotCounters = GetProcessIoCounters(GetCurrentProcess(), &ioCounters);
-  if ((gotCounters && !ioCounters.ReadOperationCount) || 
-      IsPrefetchDisabledViaService())
+
+  if (IsPrefetchDisabledViaService()) {
+    preloadReason = PRELOAD_SERVICE;
+  } else if ((gotCounters && !ioCounters.ReadOperationCount)) {
+    preloadReason = PRELOAD_IOCOUNT;
+  }
+
+  if (preloadReason != PRELOAD_NONE)
 #endif
   {
       XPCOMGlueEnablePreload();
   }
 
-
   rv = XPCOMGlueStartup(exePath);
   if (NS_FAILED(rv)) {
     Output("Couldn't load XPCOM.\n");
@@ -250,6 +261,11 @@ int main(int argc, char* argv[])
   XRE_SetupDllBlocklist();
 #endif
 
+#if defined(XP_WIN)
+  XRE_TelemetryAccumulate(mozilla::Telemetry::STARTUP_USING_PRELOAD,
+                          preloadReason);
+#endif
+
   if (gotCounters) {
 #if defined(XP_WIN)
     XRE_TelemetryAccumulate(mozilla::Telemetry::EARLY_GLUESTARTUP_READ_OPS,

toolkit/components/telemetry/TelemetryHistograms.h

@@ -85,6 +85,7 @@ HISTOGRAM(EARLY_GLUESTARTUP_READ_OPS, 1, 100, 12, LINEAR, "ProcessIoCounters.Rea
 HISTOGRAM(EARLY_GLUESTARTUP_READ_TRANSFER, 1, 50 * 1024, 12, EXPONENTIAL, "ProcessIoCounters.ReadTransferCount before glue startup (KB)")
 HISTOGRAM(GLUESTARTUP_READ_OPS, 1, 100, 12, LINEAR, "ProcessIoCounters.ReadOperationCount after glue startup")
 HISTOGRAM(GLUESTARTUP_READ_TRANSFER, 1, 50 * 1024, 12, EXPONENTIAL, "ProcessIoCounters.ReadTransferCount after glue startup (KB)")
+HISTOGRAM(STARTUP_USING_PRELOAD, 1, 2, 3, LINEAR, "Preload heuristic. 0: none, 1: preload from service, 2: preload from ioCounters.ReadOperationCount")
 #elif defined(XP_UNIX)
 HISTOGRAM(EARLY_GLUESTARTUP_HARD_FAULTS, 1, 100, 12, LINEAR, "Hard faults count before glue startup")
 HISTOGRAM(GLUESTARTUP_HARD_FAULTS, 1, 500, 12, EXPONENTIAL, "Hard faults count after glue startup")