From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751376AbVIXCzf (ORCPT ); Fri, 23 Sep 2005 22:55:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751380AbVIXCzf (ORCPT ); Fri, 23 Sep 2005 22:55:35 -0400 Received: from smtp200.mail.sc5.yahoo.com ([216.136.130.125]:36713 "HELO smtp200.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S1751376AbVIXCze (ORCPT ); Fri, 23 Sep 2005 22:55:34 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type; b=qEM1Pu0vbMWvGgyf2OAGFVZFudqqF76N3YT1RBwv4P6YwEycGwhmBJE8HD7viNQXtxzXSwphvLvXAculJrbDnzQbkrnRJG3ZlrivwruyPnmF2s0txAuOxmGCkykmYG5R8/rqnd7mM2xfL/nOyuVdpNJIv+ZRodVq6N4OzoUjigI= ; Message-ID: <4334C048.6050905@yahoo.com.au> Date: Sat, 24 Sep 2005 12:56:08 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.10) Gecko/20050802 Debian/1.7.10-1 X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton , linux-kernel CC: "David S. Miller" Subject: [PATCH 4/4] convert dec_and_lock References: <4334BCF3.1010908@yahoo.com.au> <4334BDC6.9000301@yahoo.com.au> <4334BE56.3050001@yahoo.com.au> In-Reply-To: <4334BE56.3050001@yahoo.com.au> Content-Type: multipart/mixed; boundary="------------020206020201080601020904" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------020206020201080601020904 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit 4/4 This also contains a small optimisation on UP machines where a spinlock is a noop. -- SUSE Labs, Novell Inc. --------------020206020201080601020904 Content-Type: text/plain; name="atomic-dec_and_lock-use-atomic-primitives.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="atomic-dec_and_lock-use-atomic-primitives.patch" Index: linux-2.6/lib/dec_and_lock.c =================================================================== --- linux-2.6.orig/lib/dec_and_lock.c +++ linux-2.6/lib/dec_and_lock.c @@ -1,47 +1,11 @@ #include #include #include -#include -#ifdef __HAVE_ARCH_CMPXCHG /* * This is an implementation of the notion of "decrement a * reference count, and return locked if it decremented to zero". * - * This implementation can be used on any architecture that - * has a cmpxchg, and where atomic->value is an int holding - * the value of the atomic (i.e. the high bits aren't used - * for a lock or anything like that). - */ -int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) -{ - int counter; - int newcount; - - for (;;) { - counter = atomic_read(atomic); - newcount = counter - 1; - if (!newcount) - break; /* do it the slow way */ - - newcount = cmpxchg(&atomic->counter, counter, newcount); - if (newcount == counter) - return 0; - } - - spin_lock(lock); - if (atomic_dec_and_test(atomic)) - return 1; - spin_unlock(lock); - return 0; -} -#else -/* - * This is an architecture-neutral, but slow, - * implementation of the notion of "decrement - * a reference count, and return locked if it - * decremented to zero". - * * NOTE NOTE NOTE! This is _not_ equivalent to * * if (atomic_dec_and_test(&atomic)) { @@ -52,21 +16,20 @@ int _atomic_dec_and_lock(atomic_t *atomi * * because the spin-lock and the decrement must be * "atomic". - * - * This slow version gets the spinlock unconditionally, - * and releases it if it isn't needed. Architectures - * are encouraged to come up with better approaches, - * this is trivially done efficiently using a load-locked - * store-conditional approach, for example. */ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) { +#ifdef CONFIG_SMP + /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ + if (atomic_add_unless(atomic, -1, 1)) + return 0; +#endif + /* Otherwise do it the slow way */ spin_lock(lock); if (atomic_dec_and_test(atomic)) return 1; spin_unlock(lock); return 0; } -#endif EXPORT_SYMBOL(_atomic_dec_and_lock); --------------020206020201080601020904-- Send instant messages to your online friends http://au.messenger.yahoo.com