[edk2-devel] [PATCH v1] UefiCpuPkg/SmmCpu: Refine semaphore sync between BSP and AP

["Wu, Jiaxin" <jiaxin.wu@intel.com>]

For SMM CPU semaphore sync, there is no need atomic semaphore
operation, just use the flag to indicate it has complete the
wait/release. Based on this, this patch is to refine 2 functions
(WaitForAllAPs & ReleaseAllAPs) and define 2 new functions
(WaitForBsp & ReleaseBsp) used for the semaphore sync between
BSP & AP.

Sync flow like below:
1. BSP to Release All APs ---> 1. AP to Wait BSP
   ReleaseAllAPs ()               WaitForBsp
2. BSP to Wait All APs    <--- 2. AP to Release BSP
   WaitForAllAPs ()               ReleaseBsp

With this change, SMM CPU semaphore sync for SMI exit performance
will be significant improved.

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 | 68 ++++++++++++++++++++++++++---------
 1 file changed, 51 insertions(+), 17 deletions(-)

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
index 25d058c5b9..0bf460e81c 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
@@ -120,11 +120,11 @@ LockdownSemaphore (
 
   return Value;
 }
 
 /**
-  Wait all APs to performs an atomic compare exchange operation to release semaphore.
+  Used for BSP to wait all APs.
 
   @param   NumberOfAPs      AP number
 
 **/
 VOID
@@ -133,18 +133,19 @@ WaitForAllAPs (
   )
 {
   UINTN  BspIndex;
 
   BspIndex = mSmmMpSyncData->BspIndex;
-  while (NumberOfAPs-- > 0) {
-    WaitForSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+  while (NumberOfAPs != *mSmmMpSyncData->CpuData[BspIndex].Run) {
+    CpuPause ();
   }
+
+  *mSmmMpSyncData->CpuData[BspIndex].Run = 0;
 }
 
 /**
-  Performs an atomic compare exchange operation to release semaphore
-  for each AP.
+  Used for BSP to release all APs.
 
 **/
 VOID
 ReleaseAllAPs (
   VOID
@@ -152,15 +153,48 @@ ReleaseAllAPs (
 {
   UINTN  Index;
 
   for (Index = 0; Index < mMaxNumberOfCpus; Index++) {
     if (IsPresentAp (Index)) {
-      ReleaseSemaphore (mSmmMpSyncData->CpuData[Index].Run);
+      ASSERT (*mSmmMpSyncData->CpuData[Index].Run == 0);
+      *mSmmMpSyncData->CpuData[Index].Run  = 1;
     }
   }
 }
 
+/**
+  Used for Ap to wait BSP.
+
+  @param      ApSem      IN:  32-bit unsigned integer
+                         OUT: original integer 0
+**/
+VOID
+WaitForBsp  (
+  IN OUT  volatile UINT32 *ApSem
+  )
+{
+  while (*ApSem == 0) {
+    CpuPause ();
+  }
+
+  *ApSem = 0;
+}
+
+/**
+  Used for Ap to release BSP.
+
+  @param      BspSem     IN:  32-bit unsigned integer
+                         OUT: original integer + 1
+**/
+VOID
+ReleaseBsp   (
+  IN OUT  volatile UINT32  *BspSem
+  )
+{
+  InterlockedIncrement (BspSem);
+}
+
 /**
   Check whether the index of CPU perform the package level register
   programming during System Management Mode initialization.
 
   The index of Processor specified by mPackageFirstThreadIndex[PackageIndex]
@@ -898,50 +932,50 @@ APHandler (
 
   if ((SyncMode == SmmCpuSyncModeTradition) || SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Notify BSP of arrival at this point
     //
-    ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+    ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
   }
 
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Wait for the signal from BSP to backup MTRRs
     //
-    WaitForSemaphore (mSmmMpSyncData->CpuData[CpuIndex].Run);
+    WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
 
     //
     // Backup OS MTRRs
     //
     MtrrGetAllMtrrs (&Mtrrs);
 
     //
     // Signal BSP the completion of this AP
     //
-    ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+    ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
 
     //
     // Wait for BSP's signal to program MTRRs
     //
-    WaitForSemaphore (mSmmMpSyncData->CpuData[CpuIndex].Run);
+    WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
 
     //
     // Replace OS MTRRs with SMI MTRRs
     //
     ReplaceOSMtrrs (CpuIndex);
 
     //
     // Signal BSP the completion of this AP
     //
-    ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+    ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
   }
 
   while (TRUE) {
     //
     // Wait for something to happen
     //
-    WaitForSemaphore (mSmmMpSyncData->CpuData[CpuIndex].Run);
+    WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
 
     //
     // Check if BSP wants to exit SMM
     //
     if (!(*mSmmMpSyncData->InsideSmm)) {
@@ -977,16 +1011,16 @@ APHandler (
 
   if (SmmCpuFeaturesNeedConfigureMtrrs ()) {
     //
     // Notify BSP the readiness of this AP to program MTRRs
     //
-    ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+    ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
 
     //
     // Wait for the signal from BSP to program MTRRs
     //
-    WaitForSemaphore (mSmmMpSyncData->CpuData[CpuIndex].Run);
+    WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
 
     //
     // Restore OS MTRRs
     //
     SmmCpuFeaturesReenableSmrr ();
@@ -994,26 +1028,26 @@ APHandler (
   }
 
   //
   // Notify BSP the readiness of this AP to Reset states/semaphore for this processor
   //
-  ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+  ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
 
   //
   // Wait for the signal from BSP to Reset states/semaphore for this processor
   //
-  WaitForSemaphore (mSmmMpSyncData->CpuData[CpuIndex].Run);
+  WaitForBsp (mSmmMpSyncData->CpuData[CpuIndex].Run);
 
   //
   // Reset states/semaphore for this processor
   //
   *(mSmmMpSyncData->CpuData[CpuIndex].Present) = FALSE;
 
   //
   // Notify BSP the readiness of this AP to exit SMM
   //
-  ReleaseSemaphore (mSmmMpSyncData->CpuData[BspIndex].Run);
+  ReleaseBsp (mSmmMpSyncData->CpuData[BspIndex].Run);
 }
 
 /**
   Checks whether the input token is the current used token.
 
-- 
2.16.2.windows.1



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