Re: [PATCH] UefiCpuPkg/MpInitLib: Do not wakeup AP if only one processor supported

["Tian, Feng" <feng.tian@intel.com>]

Reviewed-by: Feng Tian <feng.tian@Intel.com>

Thanks
Feng

-----Original Message-----
From: Fan, Jeff 
Sent: Friday, November 4, 2016 4:18 PM
To: edk2-devel@ml01.01.org
Cc: Tian, Feng <feng.tian@intel.com>; Gao, Liming <liming.gao@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>
Subject: [PATCH] UefiCpuPkg/MpInitLib: Do not wakeup AP if only one processor supported

If MaxLogicalProcessorNumber is only 1, we needn't to wake up APs at all and needn't to register callback functions.

It could improve boot performance on single supported system.

https://bugzilla.tianocore.org/show_bug.cgi?id=204

Cc: Feng Tian <feng.tian@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
---
 UefiCpuPkg/Library/MpInitLib/DxeMpLib.c |  7 ++++++
 UefiCpuPkg/Library/MpInitLib/MpLib.c    | 39 +++++++++++++++++++--------------
 UefiCpuPkg/Library/MpInitLib/PeiMpLib.c |  8 +++++++
 3 files changed, 37 insertions(+), 17 deletions(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
index b399f1c..eb36d6f 100644
--- a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
@@ -290,6 +290,13 @@ InitMpGlobalData (
 
   SaveCpuMpData (CpuMpData);
 
+  if (CpuMpData->CpuCount == 1) {
+    //
+    // If only BSP exists, return
+    //
+    return;
+  }
+
   //
   // Avoid APs access invalid buff data which allocated by BootServices,
   // so we will allocate reserved data for AP loop code.
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 56b870e..a0edc55 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1143,6 +1143,7 @@ MpInitLibInitialize (
   } else {
     MaxLogicalProcessorNumber = OldCpuMpData->CpuCount;
   }
+  ASSERT (MaxLogicalProcessorNumber != 0);
 
   AsmGetAddressMap (&AddressMap);
   ApResetVectorSize = AddressMap.RendezvousFunnelSize + sizeof (MP_CPU_EXCHANGE_INFO); @@ -1209,10 +1210,12 @@ MpInitLibInitialize (
   MtrrGetAllMtrrs (&CpuMpData->MtrrTable);
 
   if (OldCpuMpData == NULL) {
-    //
-    // Wakeup all APs and calculate the processor count in system
-    //
-    CollectProcessorCount (CpuMpData);
+    if (MaxLogicalProcessorNumber > 1) {
+      //
+      // Wakeup all APs and calculate the processor count in system
+      //
+      CollectProcessorCount (CpuMpData);
+    }
   } else {
     //
     // APs have been wakeup before, just get the CPU Information @@ -1238,19 +1241,21 @@ MpInitLibInitialize (
         sizeof (CPU_VOLATILE_REGISTERS)
         );
     }
-    //
-    // Wakeup APs to do some AP initialize sync
-    //
-    WakeUpAP (CpuMpData, TRUE, 0, ApInitializeSync, CpuMpData);
-    //
-    // Wait for all APs finished initialization
-    //
-    while (CpuMpData->FinishedCount < (CpuMpData->CpuCount - 1)) {
-      CpuPause ();
-    }
-    CpuMpData->InitFlag = ApInitDone;
-    for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
-      SetApState (&CpuMpData->CpuData[Index], CpuStateIdle);
+    if (MaxLogicalProcessorNumber > 1) {
+      //
+      // Wakeup APs to do some AP initialize sync
+      //
+      WakeUpAP (CpuMpData, TRUE, 0, ApInitializeSync, CpuMpData);
+      //
+      // Wait for all APs finished initialization
+      //
+      while (CpuMpData->FinishedCount < (CpuMpData->CpuCount - 1)) {
+        CpuPause ();
+      }
+      CpuMpData->InitFlag = ApInitDone;
+      for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
+        SetApState (&CpuMpData->CpuData[Index], CpuStateIdle);
+      }
     }
   }
 
diff --git a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
index e242d37..1f2fcb8 100644
--- a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
@@ -321,6 +321,14 @@ InitMpGlobalData (
   EFI_STATUS      Status;
 
   SaveCpuMpData (CpuMpData);
+
+  if (CpuMpData->CpuCount == 1) {
+    //
+    // If only BSP exists, return
+    //
+    return;
+  }
+
   //
   // Register an event for EndOfPei
   //
--
2.9.3.windows.2