From e6790e4b5d5e97dc287f3496dd2cf2dbabdfdb35 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 17 Mar 2017 20:44:45 +0100
Subject: locking/atomic/x86: Use atomic_try_cmpxchg()

Better code generation:

      text           data  bss        name
  10665111        4530096  843776     defconfig-build/vmlinux.3
  10655703        4530096  843776     defconfig-build/vmlinux.4

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/atomic64_64.h | 40 +++++++++++++-------------------------
 1 file changed, 13 insertions(+), 27 deletions(-)

(limited to 'arch/x86/include/asm/atomic64_64.h')

diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h
index 12fb57413732..6189a433c9a9 100644
--- a/arch/x86/include/asm/atomic64_64.h
+++ b/arch/x86/include/asm/atomic64_64.h
@@ -198,17 +198,12 @@ static inline long atomic64_xchg(atomic64_t *v, long new)
  */
 static inline bool atomic64_add_unless(atomic64_t *v, long a, long u)
 {
-	long c, old;
-	c = atomic64_read(v);
-	for (;;) {
-		if (unlikely(c == (u)))
-			break;
-		old = atomic64_cmpxchg((v), c, c + (a));
-		if (likely(old == c))
-			break;
-		c = old;
-	}
-	return c != (u);
+	long c = atomic64_read(v);
+	do {
+		if (unlikely(c == u))
+			return false;
+	} while (!atomic64_try_cmpxchg(v, &c, c + a));
+	return true;
 }
 
 #define atomic64_inc_not_zero(v) atomic64_add_unless((v), 1, 0)
@@ -222,17 +217,12 @@ static inline bool atomic64_add_unless(atomic64_t *v, long a, long u)
  */
 static inline long atomic64_dec_if_positive(atomic64_t *v)
 {
-	long c, old, dec;
-	c = atomic64_read(v);
-	for (;;) {
+	long dec, c = atomic64_read(v);
+	do {
 		dec = c - 1;
 		if (unlikely(dec < 0))
 			break;
-		old = atomic64_cmpxchg((v), c, dec);
-		if (likely(old == c))
-			break;
-		c = old;
-	}
+	} while (!atomic64_try_cmpxchg(v, &c, dec));
 	return dec;
 }
 
@@ -248,14 +238,10 @@ static inline void atomic64_##op(long i, atomic64_t *v)			\
 #define ATOMIC64_FETCH_OP(op, c_op)					\
 static inline long atomic64_fetch_##op(long i, atomic64_t *v)		\
 {									\
-	long old, val = atomic64_read(v);				\
-	for (;;) {							\
-		old = atomic64_cmpxchg(v, val, val c_op i);		\
-		if (old == val)						\
-			break;						\
-		val = old;						\
-	}								\
-	return old;							\
+	long val = atomic64_read(v);					\
+	do {								\
+	} while (!atomic64_try_cmpxchg(v, &val, val c_op i));		\
+	return val;							\
 }
 
 #define ATOMIC64_OPS(op, c_op)						\
-- 
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