Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932648AbVJ3Apb (ORCPT ); Sat, 29 Oct 2005 20:45:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932697AbVJ3Apb (ORCPT ); Sat, 29 Oct 2005 20:45:31 -0400 Received: from smtp207.mail.sc5.yahoo.com ([216.136.129.97]:9358 "HELO smtp207.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S932607AbVJ3Ap3 (ORCPT ); Sat, 29 Oct 2005 20:45:29 -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:Subject:References:In-Reply-To:Content-Type; b=aMzqVEE7D8NU+9bpLau1jIfK/fsCX19zJ4l4DNHbJ04IlOk61aVTwf70hC46rz48k8GxQUDrLF2KlUT2y1qLlfBy+OD+i/9NgAwDufjtRBxKZIbGESnubaCQV7UWfAAc7jP3ZC0f62ZppMOfbV50iyGjq1ELWvkbUNqT+rf8B/8= ; Message-ID: <43641808.5000705@yahoo.com.au> Date: Sun, 30 Oct 2005 11:47:04 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: linux-kernel Subject: [patch 5/5] atomic: dec_and_lock use atomic primitives References: <436416AD.3050709@yahoo.com.au> <4364171C.7020103@yahoo.com.au> <43641755.5010004@yahoo.com.au> <4364178E.8040502@yahoo.com.au> <436417C2.3050703@yahoo.com.au> In-Reply-To: <436417C2.3050703@yahoo.com.au> Content-Type: multipart/mixed; boundary="------------010502050602010205070501" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3033 Lines: 106 This is a multi-part message in MIME format. --------------010502050602010205070501 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit 5/5 -- SUSE Labs, Novell Inc. --------------010502050602010205070501 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); --------------010502050602010205070501-- Send instant messages to your online friends http://au.messenger.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/