From 8057048cbc4e0ee60a36cb5c93b2cf58291cfbc3 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 12:39:07 +0200
Subject: [PATCH] --- yaml --- r: 155211 b: refs/heads/master c:
 824975ef190e7dcb77718d1cc2cb53769b16d918 h: refs/heads/master i:   155209:
 971bdf050b2a65802609c771980fc8556f084923   155207:
 937a0037421902186e410e0e9f45562f30489c2c v: v3

---
 [refs]                           |  2 +-
 trunk/arch/x86/lib/atomic64_32.c | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 7b25ffc3982e..d5f9b5c562f4 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 69237f94e65d3d7f539f1adb98ef68685c595004
+refs/heads/master: 824975ef190e7dcb77718d1cc2cb53769b16d918
diff --git a/trunk/arch/x86/lib/atomic64_32.c b/trunk/arch/x86/lib/atomic64_32.c
index 5fc1e2caa544..61959627e1e1 100644
--- a/trunk/arch/x86/lib/atomic64_32.c
+++ b/trunk/arch/x86/lib/atomic64_32.c
@@ -76,13 +76,22 @@ u64 atomic64_read(atomic64_t *ptr)
  */
 u64 atomic64_add_return(u64 delta, atomic64_t *ptr)
 {
-	u64 old_val, new_val;
+	/*
+	 * Try first with a (probably incorrect) assumption about
+	 * what we have there. We'll do two loops most likely,
+	 * but we'll get an ownership MESI transaction straight away
+	 * instead of a read transaction followed by a
+	 * flush-for-ownership transaction:
+	 */
+	u64 old_val, new_val, real_val = 1ULL << 32;
 
 	do {
-		old_val = atomic_read(ptr);
+		old_val = real_val;
 		new_val = old_val + delta;
 
-	} while (atomic64_cmpxchg(ptr, old_val, new_val) != old_val);
+		real_val = atomic64_cmpxchg(ptr, old_val, new_val);
+
+	} while (real_val != old_val);
 
 	return new_val;
 }