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From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de, hpa@zytor.com
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	arjan@linux.intel.com, bp@alien8.de,
	richard.weinberger@gmail.com, jpoimboe@redhat.com,
	peterz@infradead.org
Subject: [PATCH 4/5] refcount: Use atomic_try_cmpxchg()
Date: Fri, 17 Mar 2017 22:19:22 +0100	[thread overview]
Message-ID: <20170317212350.974054153@infradead.org> (raw)
In-Reply-To: 20170317211918.393791494@infradead.org

[-- Attachment #1: peterz-ref-6.patch --]
[-- Type: text/plain, Size: 3081 bytes --]

Generates better code (GCC-6.2.1):

   text    data     bss     dec     hex filename
   1576       7       0    1583     62f defconfig-build/lib/refcount.o.pre
   1488       7       0    1495     5d7 defconfig-build/lib/refcount.o.post

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 lib/refcount.c |   47 +++++++++++++++--------------------------------
 1 file changed, 15 insertions(+), 32 deletions(-)

--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -57,9 +57,9 @@
  */
 bool refcount_add_not_zero(unsigned int i, refcount_t *r)
 {
-	unsigned int old, new, val = atomic_read(&r->refs);
+	unsigned int new, val = atomic_read(&r->refs);
 
-	for (;;) {
+	do {
 		if (!val)
 			return false;
 
@@ -69,12 +69,8 @@ bool refcount_add_not_zero(unsigned int
 		new = val + i;
 		if (new < val)
 			new = UINT_MAX;
-		old = atomic_cmpxchg_relaxed(&r->refs, val, new);
-		if (old == val)
-			break;
 
-		val = old;
-	}
+	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
 
 	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
 
@@ -118,9 +114,9 @@ EXPORT_SYMBOL_GPL(refcount_add);
  */
 bool refcount_inc_not_zero(refcount_t *r)
 {
-	unsigned int old, new, val = atomic_read(&r->refs);
+	unsigned int new, val = atomic_read(&r->refs);
 
-	for (;;) {
+	do {
 		new = val + 1;
 
 		if (!val)
@@ -129,12 +125,7 @@ bool refcount_inc_not_zero(refcount_t *r
 		if (unlikely(!new))
 			return true;
 
-		old = atomic_cmpxchg_relaxed(&r->refs, val, new);
-		if (old == val)
-			break;
-
-		val = old;
-	}
+	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
 
 	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
 
@@ -182,9 +173,9 @@ EXPORT_SYMBOL_GPL(refcount_inc);
  */
 bool refcount_sub_and_test(unsigned int i, refcount_t *r)
 {
-	unsigned int old, new, val = atomic_read(&r->refs);
+	unsigned int new, val = atomic_read(&r->refs);
 
-	for (;;) {
+	do {
 		if (unlikely(val == UINT_MAX))
 			return false;
 
@@ -194,12 +185,7 @@ bool refcount_sub_and_test(unsigned int
 			return false;
 		}
 
-		old = atomic_cmpxchg_release(&r->refs, val, new);
-		if (old == val)
-			break;
-
-		val = old;
-	}
+	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
 
 	return !new;
 }
@@ -258,7 +244,9 @@ EXPORT_SYMBOL_GPL(refcount_dec);
  */
 bool refcount_dec_if_one(refcount_t *r)
 {
-	return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;
+	int val = 1;
+
+	return atomic_try_cmpxchg_release(&r->refs, &val, 0);
 }
 EXPORT_SYMBOL_GPL(refcount_dec_if_one);
 
@@ -275,9 +263,9 @@ EXPORT_SYMBOL_GPL(refcount_dec_if_one);
  */
 bool refcount_dec_not_one(refcount_t *r)
 {
-	unsigned int old, new, val = atomic_read(&r->refs);
+	unsigned int new, val = atomic_read(&r->refs);
 
-	for (;;) {
+	do {
 		if (unlikely(val == UINT_MAX))
 			return true;
 
@@ -290,12 +278,7 @@ bool refcount_dec_not_one(refcount_t *r)
 			return true;
 		}
 
-		old = atomic_cmpxchg_release(&r->refs, val, new);
-		if (old == val)
-			break;
-
-		val = old;
-	}
+	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
 
 	return true;
 }

  parent reply	other threads:[~2017-03-17 21:31 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-17 21:19 [PATCH 0/5] x86 optimizations Peter Zijlstra
2017-03-17 21:19 ` [PATCH 1/5] x86: Implement __WARN using UD0 Peter Zijlstra
2017-03-21 14:03   ` Josh Poimboeuf
2017-03-21 15:14     ` Peter Zijlstra
2017-03-21 15:17       ` Arjan van de Ven
2017-03-21 15:32       ` Josh Poimboeuf
2017-03-21 15:41         ` Peter Zijlstra
2017-03-22  8:47     ` Peter Zijlstra
2017-03-22 14:18       ` Josh Poimboeuf
2017-03-17 21:19 ` [PATCH 2/5] bug: Add _ONCE logic to report_bug() Peter Zijlstra
2017-03-17 21:19 ` [PATCH 3/5] atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra
2017-03-17 21:19 ` Peter Zijlstra [this message]
2017-03-17 21:19 ` [PATCH 5/5] x86,atomic: Use atomic_try_cmpxchg Peter Zijlstra

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