After review, there are unnecessary steps for BSP and AP sync for exit.
This patch is to reduce one round BSP and AP sync for exit so as to
improve SMM performance:
WaitForAllAPs <- ReleaseBsp
ReleaseAllAPs -> WaitForBsp

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zeng Star <star.zeng@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
---
 UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 44 +++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
index e96c7f51d6..5a42a5dd12 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
@@ -665,11 +665,13 @@ BSPHandler (
     //
     *mSmmMpSyncData->AllCpusInSync = TRUE;
     ApCount                        = LockdownSemaphore (mSmmMpSyncData->Counter) - 1;
 
     //
-    // Wait for all APs to get ready for programming MTRRs
+    // Wait for all APs:
+    // 1. Make sure all Aps have set the Present.
+    // 2. Get ready for programming MTRRs.
     //
     WaitForAllAPs (ApCount);
 
     if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
       //
@@ -768,16 +770,16 @@ BSPHandler (
   // Notify all APs to exit
   //
   *mSmmMpSyncData->InsideSmm = FALSE;
   ReleaseAllAPs ();
 
-  //
-  // Wait for all APs to complete their pending tasks
-  //
-  WaitForAllAPs (ApCount);
-
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
+    //
+    // Wait for all APs to complete their pending tasks
+    //
+    WaitForAllAPs (ApCount);
+
     //
     // Signal APs to restore MTRRs
     //
     ReleaseAllAPs ();
 
@@ -789,23 +791,23 @@ BSPHandler (
 
     //
     // Wait for all APs to complete MTRR programming
     //
     WaitForAllAPs (ApCount);
+
+    //
+    // Signal APs to Reset states/semaphore for this processor
+    //
+    ReleaseAllAPs ();
   }
 
   //
   // Stop source level debug in BSP handler, the code below will not be
   // debugged.
   //
   InitializeDebugAgent (DEBUG_AGENT_INIT_EXIT_SMI, NULL, NULL);
 
-  //
-  // Signal APs to Reset states/semaphore for this processor
-  //
-  ReleaseAllAPs ();
-
   //
   // Perform pending operations for hot-plug
   //
   SmmCpuUpdate ();
 
@@ -941,10 +943,12 @@ APHandler (
   *(mSmmMpSyncData->CpuData[CpuIndex].Present) = TRUE;
 
   if ((SyncMode == SmmCpuSyncModeTradition) || SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Notify BSP of arrival at this point
+    // 1. Set the Present.
+    // 2. Get ready for programming MTRRs.
     //
     ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
   }
 
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
@@ -1033,21 +1037,21 @@ APHandler (
     //
     // Restore OS MTRRs
     //
     SmmCpuFeaturesReenableSmrr ();
     MtrrSetAllMtrrs (&Mtrrs);
-  }
 
-  //
-  // Notify BSP the readiness of this AP to Reset states/semaphore for this processor
-  //
-  ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
+    //
+    // Notify BSP the readiness of this AP to Reset states/semaphore for this processor
+    //
+    ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
 
-  //
-  // Wait for the signal from BSP to Reset states/semaphore for this processor
-  //
-  WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
+    //
+    // Wait for the signal from BSP to Reset states/semaphore for this processor
+    //
+    WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
+  }
 
   //
   // Reset states/semaphore for this processor
   //
   *(mSmmMpSyncData->CpuData[CpuIndex].Present) = FALSE;
-- 
2.16.2.windows.1



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