From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757355AbcLOE6V (ORCPT ); Wed, 14 Dec 2016 23:58:21 -0500 Received: from frisell.zx2c4.com ([192.95.5.64]:55691 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753565AbcLOE6T (ORCPT ); Wed, 14 Dec 2016 23:58:19 -0500 From: "Jason A. Donenfeld" To: Dave Airlie , linux-kernel@vger.kernel.org, Thomas Hellstrom Cc: "Jason A. Donenfeld" Subject: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless Date: Thu, 15 Dec 2016 05:58:10 +0100 Message-Id: <20161215045810.3065-1-Jason@zx2c4.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <561ABFA6.8050102@vmware.com> References: <561ABFA6.8050102@vmware.com> 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 Reviewed-by: Thomas Hellstrom --- This was reviewed favorably 14 months ago but never picked up. I'm resubmitting it now in hopes that you can finally queue it up for 4.10. 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 e15828fd71f1..62f0a84ae94e 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -133,6 +133,6 @@ 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_ */ -- 2.11.0