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diff --git a/PerformancePkg/Library/TscTimerLib/BaseTscTimerLib.c b/PerformancePkg/Library/TscTimerLib/BaseTscTimerLib.c
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+++ b/PerformancePkg/Library/TscTimerLib/BaseTscTimerLib.c
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+/** @file
+  A Base Timer Library implementation which uses the Time Stamp Counter in the processor.
+
+  For Pentium 4 processors, Intel Xeon processors (family [0FH], models [03H and higher]);
+    for Intel Core Solo and Intel Core Duo processors (family [06H], model [0EH]);
+    for the Intel Xeon processor 5100 series and Intel Core 2 Duo processors (family [06H], model [0FH]);
+    for Intel Core 2 and Intel Xeon processors (family [06H], display_model [17H]);
+    for Intel Atom processors (family [06H], display_model [1CH]):
+  the time-stamp counter increments at a constant rate.
+  That rate may be set by the maximum core-clock to bus-clock ratio of the processor or may be set by
+  the maximum resolved frequency at which the processor is booted. The maximum resolved frequency may
+  differ from the maximum qualified frequency of the processor.
+
+  The specific processor configuration determines the behavior. Constant TSC behavior ensures that the
+  duration of each clock tick is uniform and supports the use of the TSC as a wall clock timer even if
+  the processor core changes frequency. This is the architectural behavior moving forward.
+
+  A Processor's support for invariant TSC is indicated by CPUID.0x80000007.EDX[8].
+
+  Copyright (c) 2009 - 2011, Intel Corporation. All rights reserved.<BR>
+  This program and the accompanying materials
+  are licensed and made available under the terms and conditions of the BSD License
+  which accompanies this distribution. The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include "TscTimerLibInternal.h"
+
+UINT64  mTscFrequency = 0;
+
+/**  Get TSC frequency.
+
+  @return The number of TSC counts per second.
+
+**/
+UINT64
+InternalGetTscFrequency (
+  VOID
+  )
+{
+  UINT64    TscFrequency;
+
+  if (mTscFrequency != 0) {
+    return mTscFrequency;
+  }
+
+  TscFrequency = InternalCalculateTscFrequency ();
+
+  mTscFrequency = TscFrequency;
+
+  return TscFrequency;
+}
+