From 14e8137c8223f6d78135af6180b5e3145351da17 Mon Sep 17 00:00:00 2001
From: Jeff Fan <jeff.fan@intel.com>
Date: Fri, 4 Nov 2016 15:45:13 +0800
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>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Feng Tian <feng.tian@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 b399f1c24d..eb36d6f78d 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 56b870e527..a0edc55f52 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 e242d37b3b..1f2fcb8b1c 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
   //
-- 
2.39.2