Remove some unnecessary spinning

src/System.Private.CoreLib/shared/System/Collections/Concurrent/ConcurrentQueueSegment.cs

@@ -112,15 +112,13 @@ internal static int RoundUpToPowerOf2(int i)
                 _frozenForEnqueues = true;
 
                 // Increase the tail by FreezeOffset, spinning until we're successful in doing so.
-                var spinner = new SpinWait();
                 while (true)
                 {
                     int tail = Volatile.Read(ref _headAndTail.Tail);
                     if (Interlocked.CompareExchange(ref _headAndTail.Tail, tail + FreezeOffset, tail) == tail)
                     {
                         break;
                     }
-                    spinner.SpinOnce();
                 }
             }
         }

src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs

@@ -721,7 +721,6 @@ internal bool AtomicStateUpdate(int newBits, int illegalBits)
 
         private bool AtomicStateUpdateSlow(int newBits, int illegalBits)
         {
-            var sw = new SpinWait();
             do
             {
                 int oldFlags = m_stateFlags;
@@ -730,13 +729,11 @@ private bool AtomicStateUpdateSlow(int newBits, int illegalBits)
                 {
                     return true;
                 }
-                sw.SpinOnce();
             } while (true);
         }
 
         internal bool AtomicStateUpdate(int newBits, int illegalBits, ref int oldFlags)
         {
-            SpinWait sw = new SpinWait();
             do
             {
                 oldFlags = m_stateFlags;
@@ -745,7 +742,6 @@ internal bool AtomicStateUpdate(int newBits, int illegalBits, ref int oldFlags)
                 {
                     return true;
                 }
-                sw.SpinOnce();
             } while (true);
         }
 
@@ -772,13 +768,11 @@ internal void SetNotificationForWaitCompletion(bool enabled)
             else
             {
                 // Atomically clear the END_AWAIT_NOTIFICATION bit
-                SpinWait sw = new SpinWait();
                 while (true)
                 {
                     int oldFlags = m_stateFlags;
                     int newFlags = oldFlags & (~TASK_STATE_WAIT_COMPLETION_NOTIFICATION);
                     if (Interlocked.CompareExchange(ref m_stateFlags, newFlags, oldFlags) == oldFlags) break;
-                    sw.SpinOnce();
                 }
             }
         }