From 0f18e1eda2a807283484adfbf5eaae6a92b1ffa7 Mon Sep 17 00:00:00 2001
From: Jeff Fan <jeff.fan@intel.com>
Date: Mon, 21 Mar 2016 13:26:46 +0800
Subject: MdePkg/BaseSynchronizationLib: Do not check timeout if lock released

Current AcquireSpinLock() will check if timeout happens when PcdSpinLockTimeout
is not zero, even though the spin lock is already released. It may do
unnecessary operation to read timer's counter. This update is trying to acquire
spin lock firstly. If it could be acquired successfully, needn't to check
timeout at all.

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
---
 MdePkg/Library/BaseSynchronizationLib/Synchronization.c    | 12 ++++++------
 MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c | 12 ++++++------
 MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c | 12 ++++++------
 3 files changed, 18 insertions(+), 18 deletions(-)

(limited to 'MdePkg/Library/BaseSynchronizationLib')

diff --git a/MdePkg/Library/BaseSynchronizationLib/Synchronization.c b/MdePkg/Library/BaseSynchronizationLib/Synchronization.c
index 4218a265a0..bb0c8e9469 100644
--- a/MdePkg/Library/BaseSynchronizationLib/Synchronization.c
+++ b/MdePkg/Library/BaseSynchronizationLib/Synchronization.c
@@ -1,7 +1,7 @@
 /** @file
   Implementation of synchronization functions.
 
-  Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2016, 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
@@ -104,7 +104,11 @@ AcquireSpinLock (
   INT64   Cycle;
   INT64   Delta;
 
-  if (PcdGet32 (PcdSpinLockTimeout) > 0) {
+  if (PcdGet32 (PcdSpinLockTimeout) == 0) {
+    while (!AcquireSpinLockOrFail (SpinLock)) {
+      CpuPause ();
+    }
+  } else if (!AcquireSpinLockOrFail (SpinLock)) {
     //
     // Get the current timer value
     //
@@ -148,10 +152,6 @@ AcquireSpinLock (
       Total += Delta;
       ASSERT (Total < Timeout);
     }
-  } else {
-    while (!AcquireSpinLockOrFail (SpinLock)) {
-      CpuPause ();
-    }
   }
   return SpinLock;
 }
diff --git a/MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c b/MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c
index 587f5a771c..31f28ec2c5 100644
--- a/MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c
+++ b/MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c
@@ -1,7 +1,7 @@
 /** @file
   Implementation of synchronization functions.
 
-  Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
   Portions copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
@@ -114,7 +114,11 @@ AcquireSpinLock (
   INT64   Cycle;
   INT64   Delta;
 
-  if (PcdGet32 (PcdSpinLockTimeout) > 0) {
+  if (PcdGet32 (PcdSpinLockTimeout) == 0) {
+    while (!AcquireSpinLockOrFail (SpinLock)) {
+      CpuPause ();
+    }
+  } else if (!AcquireSpinLockOrFail (SpinLock)) {
     //
     // Get the current timer value
     //
@@ -158,10 +162,6 @@ AcquireSpinLock (
       Total += Delta;
       ASSERT (Total < Timeout);
     }
-  } else {
-    while (!AcquireSpinLockOrFail (SpinLock)) {
-      CpuPause ();
-    }
   }
   return SpinLock;
 }
diff --git a/MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c b/MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c
index ca21f5dcce..821c798121 100644
--- a/MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c
+++ b/MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c
@@ -1,7 +1,7 @@
 /** @file
   Implementation of synchronization functions.
 
-  Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2016, 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
@@ -116,7 +116,11 @@ AcquireSpinLock (
   INT64   Cycle;
   INT64   Delta;
 
-  if (PcdGet32 (PcdSpinLockTimeout) > 0) {
+  if (PcdGet32 (PcdSpinLockTimeout) == 0) {
+    while (!AcquireSpinLockOrFail (SpinLock)) {
+      CpuPause ();
+    }
+  } else if (!AcquireSpinLockOrFail (SpinLock)) {
     //
     // Get the current timer value
     //
@@ -160,10 +164,6 @@ AcquireSpinLock (
       Total += Delta;
       ASSERT (Total < Timeout);
     }
-  } else {
-    while (!AcquireSpinLockOrFail (SpinLock)) {
-      CpuPause ();
-    }
   }
   return SpinLock;
 }
-- 
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