From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752614AbZAYUu2 (ORCPT ); Sun, 25 Jan 2009 15:50:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751151AbZAYUuR (ORCPT ); Sun, 25 Jan 2009 15:50:17 -0500 Received: from ug-out-1314.google.com ([66.249.92.174]:5631 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751127AbZAYUuP (ORCPT ); Sun, 25 Jan 2009 15:50:15 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:cc:subject; b=c+0E/0+ahzzfsUpgVSzCNWwbtNE5L1jF2+p2+EXeP4cQ8Gel26D8htEzzyQTiqR7sq UrEjM5DIVWLnKSiEkBGDNcZiv/4lwYj+vZvID83iA06Lo4JGEN9wTo68iBMpc+fllOto AZCygXaqmXvTgE2sxv3Sr7CyfDmo60Sia82do= Message-ID: <497cd085.2283420a.5373.49e7@mx.google.com> Date: Sun, 25 Jan 2009 12:50:13 -0800 (PST) From: Frederic Weisbecker To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Frederic Weisbecker Subject: [PATCH 1/2] x86: optimize a bit __raw_read_trylock Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current version of __raw_read_trylock starts with decrementing the lock and read its new value as a separate operation after that. That makes 3 dereferences (read, write (after sub), read) whereas a single atomic_dec_return does only two pointers dereferences (read, write). Signed-off-by: Frederic Weisbecker --- arch/x86/include/asm/spinlock.h | 3 +-- 1 files changed, 1 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 2bd6b11..139b424 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -267,8 +267,7 @@ static inline int __raw_read_trylock(raw_rwlock_t *lock) { atomic_t *count = (atomic_t *)lock; - atomic_dec(count); - if (atomic_read(count) >= 0) + if (atomic_dec_return(count) >= 0) return 1; atomic_inc(count); return 0; -- 1.6.1