From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751820AbbJJK4y (ORCPT ); Sat, 10 Oct 2015 06:56:54 -0400 Received: from frisell.zx2c4.com ([192.95.5.64]:48874 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751380AbbJJK4x (ORCPT ); Sat, 10 Oct 2015 06:56:53 -0400 From: "Jason A. Donenfeld" To: Dave Airlie , Thomas Hellstrom , linux-kernel@vger.kernel.org Cc: "Jason A. Donenfeld" Subject: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless Date: Sat, 10 Oct 2015 12:56:34 +0200 Message-Id: <1444474594-28359-1-git-send-email-Jason@zx2c4.com> X-Mailer: git-send-email 2.6.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On most platforms, there exists this ifdef: #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) This makes this patch functionally useless. However, on PPC, there is actually an explicit definition of atomic_inc_not_zero with its own assembly that is slightly more optimized than atomic_add_unless. So, this patch changes kref to use atomic_inc_not_zero instead, for PPC and any future platforms that might provide an explicit implementation. This also puts this usage of kref more in line with a verbatim reading of the examples in Paul McKenney's paper [1] in the section titled "2.4 Atomic Counting With Check and Release Memory Barrier", which uses atomic_inc_not_zero. [1] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf Signed-off-by: Jason A. Donenfeld --- include/linux/kref.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kref.h b/include/linux/kref.h index 484604d..83d1f94 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -166,6 +166,6 @@ static inline int kref_put_mutex(struct kref *kref, */ static inline int __must_check kref_get_unless_zero(struct kref *kref) { - return atomic_add_unless(&kref->refcount, 1, 0); + return atomic_inc_not_zero(&kref->refcount); } #endif /* _KREF_H_ */ -- 2.6.0