Fix hill climbing float overflow (dotnet/coreclr#14505)

Fix hill climbing float overflow

- When hill climbing finds that it wants to decrease the thread count but can't because the thread count is already the minimum, it instead tries to increase the sampling interval by a factor of up to 10 depending on how much it wanted to decrease the thread count
- The ratio was being used incorrectly (used max instead of min), and sometimes the ratio can be so large that the conversion to int after the float math overflows
- If something in the process enabled floating point exceptions, it may also crash
  - There doesn't appear to be a clean way to disable hill climbing, added a config variable that disables it in case a workaround is necessary for some other reason in the future
- Fixed to avoid overflow in the math to what was probably intended
- There may be another bug in GetWaveComponent() that causes values of such high magnitude to be generated, I'll leave that investigation for when that in particular becomes a real issue

Commit migrated from dotnet/coreclr@a589e39

src/coreclr/src/inc/clrconfigvalues.h

@@ -874,6 +874,7 @@ RETAIL_CONFIG_DWORD_INFO(EXTERNAL_Thread_UseAllCpuGroups, W("Thread_UseAllCpuGro
 
 CONFIG_DWORD_INFO(INTERNAL_ThreadpoolTickCountAdjustment, W("ThreadpoolTickCountAdjustment"), 0, "")
 
+RETAIL_CONFIG_DWORD_INFO(INTERNAL_HillClimbing_Disable,                             W("HillClimbing_Disable"),                            0, "Disables hill climbing for thread adjustments in the thread pool");
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_HillClimbing_WavePeriod,                          W("HillClimbing_WavePeriod"),                         4, "");
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_HillClimbing_TargetSignalToNoiseRatio,            W("HillClimbing_TargetSignalToNoiseRatio"),           300, "");
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_HillClimbing_ErrorSmoothingFactor,                W("HillClimbing_ErrorSmoothingFactor"),               1, "");

src/coreclr/src/vm/hillclimbing.cpp

@@ -335,7 +335,7 @@ int HillClimbing::Update(int currentThreadCount, double sampleDuration, int numC
     // we'll simply stay at minThreads much longer, and only occasionally try a higher value.
     //
     if (ratio.r < 0.0 && newThreadCount == ThreadpoolMgr::MinLimitTotalWorkerThreads)
-        *pNewSampleInterval = (int)(0.5 + m_currentSampleInterval * (10.0 * max(-ratio.r, 1.0)));
+        *pNewSampleInterval = (int)(0.5 + m_currentSampleInterval * (10.0 * min(-ratio.r, 1.0)));
     else
         *pNewSampleInterval = m_currentSampleInterval; 
 

src/coreclr/src/vm/win32threadpool.cpp

@@ -104,6 +104,7 @@ DWORD ThreadpoolMgr::NextCompletedWorkRequestsTime;
 LARGE_INTEGER ThreadpoolMgr::CurrentSampleStartTime;
 
 unsigned int ThreadpoolMgr::WorkerThreadSpinLimit;
+bool ThreadpoolMgr::IsHillClimbingDisabled;
 int ThreadpoolMgr::ThreadAdjustmentInterval;
 
 #define INVALID_HANDLE ((HANDLE) -1)
@@ -355,6 +356,7 @@ BOOL ThreadpoolMgr::Initialize()
     EX_TRY
     {
         WorkerThreadSpinLimit = CLRConfig::GetConfigValue(CLRConfig::INTERNAL_ThreadPool_UnfairSemaphoreSpinLimit);
+        IsHillClimbingDisabled = CLRConfig::GetConfigValue(CLRConfig::INTERNAL_HillClimbing_Disable) != 0;
         ThreadAdjustmentInterval = CLRConfig::GetConfigValue(CLRConfig::INTERNAL_HillClimbing_SampleIntervalLow);
 
         pADTPCount->InitResources();

src/coreclr/src/vm/win32threadpool.h

@@ -861,7 +861,7 @@ class ThreadpoolMgr
         {
             ThreadCounter::Counts counts = WorkerCounter.GetCleanCounts();
             if (counts.NumActive <= counts.MaxWorking)
-                return true;
+                return !IsHillClimbingDisabled;
         }
 
         return false;
@@ -1025,6 +1025,7 @@ class ThreadpoolMgr
     static LARGE_INTEGER CurrentSampleStartTime;
 
     static unsigned int WorkerThreadSpinLimit;
+    static bool IsHillClimbingDisabled;
     static int ThreadAdjustmentInterval;
 
     SPTR_DECL(WorkRequest,WorkRequestHead);             // Head of work request queue