From 6cfd3b358816722cc51f061f774baa1b36f56233 Mon Sep 17 00:00:00 2001
From: Eduardo Velarde <eduardo.velarde@pucp.pe>
Date: Wed, 20 Mar 2024 17:49:34 -0700
Subject: [PATCH] Add initialization for yield normalization

---
 src/coreclr/vm/ceemain.cpp                  |  4 ++
 src/coreclr/vm/yieldprocessornormalized.cpp | 48 +++++++++++++++------
 2 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/src/coreclr/vm/ceemain.cpp b/src/coreclr/vm/ceemain.cpp
index 0e546ffa120630..9fffba0f4f9d57 100644
--- a/src/coreclr/vm/ceemain.cpp
+++ b/src/coreclr/vm/ceemain.cpp
@@ -779,6 +779,10 @@ void EEStartupHelper()
         StubPrecode::StaticInitialize();
         FixupPrecode::StaticInitialize();
 
+        // Perform some measurements before garbage collector is initialized
+        // so GC initialization and the first few GCs can use the normalized yield
+        YieldProcessorNormalization::PerformMeasurement();
+
         InitializeGarbageCollector();
 
         if (!GCHandleUtilities::GetGCHandleManager()->Initialize())
diff --git a/src/coreclr/vm/yieldprocessornormalized.cpp b/src/coreclr/vm/yieldprocessornormalized.cpp
index 14166de34dd641..282601a435a452 100644
--- a/src/coreclr/vm/yieldprocessornormalized.cpp
+++ b/src/coreclr/vm/yieldprocessornormalized.cpp
@@ -10,12 +10,14 @@
 enum class NormalizationState : UINT8
 {
     Uninitialized,
+    PartiallyInitialized,
     Initialized,
     Failed
 };
 
 static const int NsPerYieldMeasurementCount = 8;
 static const unsigned int MeasurementPeriodMs = 4000;
+static const int s_partialInitializationMeasurementCount = 2; // number of measurements to be done during partial initialization
 
 static const unsigned int NsPerS = 1000 * 1000 * 1000;
 
@@ -118,9 +120,9 @@ void YieldProcessorNormalization::PerformMeasurement()
     }
     CONTRACTL_END;
 
-    _ASSERTE(s_isMeasurementScheduled);
+    _ASSERTE(s_isMeasurementScheduled ^ (s_normalizationState == NormalizationState::Uninitialized));
 
-    double latestNsPerYield;
+    double latestNsPerYield = 0; // initialize to supress error C4701
     if (s_normalizationState == NormalizationState::Initialized)
     {
         if (GetTickCount() - s_previousNormalizationTimeMs < MeasurementPeriodMs)
@@ -137,19 +139,31 @@ void YieldProcessorNormalization::PerformMeasurement()
         }
         s_nextMeasurementIndex = nextMeasurementIndex;
     }
-    else if (s_normalizationState == NormalizationState::Uninitialized)
+    else if (s_normalizationState == NormalizationState::Uninitialized || s_normalizationState == NormalizationState::PartiallyInitialized)
     {
-        LARGE_INTEGER li;
-        if (!QueryPerformanceFrequency(&li) || li.QuadPart < 1000 * 1000)
+        int startIndex, endIndex;
+        if (s_normalizationState == NormalizationState::Uninitialized)
         {
-            // High precision clock not available or clock resolution is too low, resort to defaults
-            s_normalizationState = NormalizationState::Failed;
-            return;
+            LARGE_INTEGER li;
+            if (!QueryPerformanceFrequency(&li) || li.QuadPart < 1000 * 1000)
+            {
+                // High precision clock not available or clock resolution is too low, resort to defaults
+                s_normalizationState = NormalizationState::Failed;
+                return;
+            }
+            s_performanceCounterTicksPerS = li.QuadPart;
+
+            startIndex = 0;
+            endIndex = s_partialInitializationMeasurementCount;
+        }
+        else
+        {
+            startIndex = s_partialInitializationMeasurementCount;
+            endIndex = NsPerYieldMeasurementCount;
         }
-        s_performanceCounterTicksPerS = li.QuadPart;
 
         unsigned int measureDurationUs = DetermineMeasureDurationUs();
-        for (int i = 0; i < NsPerYieldMeasurementCount; ++i)
+        for (int i = startIndex; i < endIndex; ++i)
         {
             latestNsPerYield = MeasureNsPerYield(measureDurationUs);
             AtomicStore(&s_nsPerYieldMeasurements[i], latestNsPerYield);
@@ -163,6 +177,11 @@ void YieldProcessorNormalization::PerformMeasurement()
                 FireEtwYieldProcessorMeasurement(GetClrInstanceId(), latestNsPerYield, s_establishedNsPerYield);
             }
         }
+
+        s_normalizationState =
+            (s_normalizationState == NormalizationState::Uninitialized) ?
+            NormalizationState::PartiallyInitialized :
+            NormalizationState::Initialized;
     }
     else
     {
@@ -171,7 +190,11 @@ void YieldProcessorNormalization::PerformMeasurement()
     }
 
     double establishedNsPerYield = s_nsPerYieldMeasurements[0];
-    for (int i = 1; i < NsPerYieldMeasurementCount; ++i)
+    int endIndex =
+        (s_normalizationState == NormalizationState::PartiallyInitialized) ?
+        s_partialInitializationMeasurementCount :
+        NsPerYieldMeasurementCount;
+    for (int i = 1; i < endIndex; ++i)
     {
         double nsPerYield = s_nsPerYieldMeasurements[i];
         if (nsPerYield < establishedNsPerYield)
@@ -201,7 +224,6 @@ void YieldProcessorNormalization::PerformMeasurement()
     GCHeapUtilities::GetGCHeap()->SetYieldProcessorScalingFactor((float)yieldsPerNormalizedYield);
 
     s_previousNormalizationTimeMs = GetTickCount();
-    s_normalizationState = NormalizationState::Initialized;
     s_isMeasurementScheduled = false;
 }
 
@@ -217,7 +239,7 @@ void YieldProcessorNormalization::ScheduleMeasurementIfNecessary()
     CONTRACTL_END;
 
     NormalizationState normalizationState = VolatileLoadWithoutBarrier(&s_normalizationState);
-    if (normalizationState == NormalizationState::Initialized)
+    if (normalizationState == NormalizationState::Initialized || normalizationState == NormalizationState::PartiallyInitialized)
     {
         if (GetTickCount() - s_previousNormalizationTimeMs < MeasurementPeriodMs)
         {