From patchwork Fri Jul 12 06:32:51 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: pingfan liu X-Patchwork-Id: 258693 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id A453C2C0091 for ; Fri, 12 Jul 2013 16:33:52 +1000 (EST) Received: from localhost ([::1]:39398 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UxWvO-0006yt-Jb for incoming@patchwork.ozlabs.org; Fri, 12 Jul 2013 02:33:50 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35703) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UxWvA-0006yl-RE for qemu-devel@nongnu.org; Fri, 12 Jul 2013 02:33:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UxWv9-00067A-O2 for qemu-devel@nongnu.org; Fri, 12 Jul 2013 02:33:36 -0400 Received: from mail-oa0-x233.google.com ([2607:f8b0:4003:c02::233]:47369) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UxWv9-00066e-JD for qemu-devel@nongnu.org; Fri, 12 Jul 2013 02:33:35 -0400 Received: by mail-oa0-f51.google.com with SMTP id i4so12208243oah.24 for ; Thu, 11 Jul 2013 23:33:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:x-mailer; bh=kVTyGiBr8TD7zgHF0PBOeeLOk449nqojZjg/KWcogjs=; b=TQOMHmxhRsuOER0jeUf03bozf9r4QwRIKa/cPUNZsIDg+9ZoLb/8xk33t6ZCZr33Ru hIcc7vLGipNgAuBNaQsLsRcJFuvydZYi6cGiShQ3TBewmJ8wsnF6p/6SgSSpm5Pl5jhv pGpLNL2xjIid4Bl4KbC30B8/Ub0Qf1W2lCueVIuA0LYdoB5hY/PGMjyF7aEwGUEGg7st lvJVJ45tQeKqOb4IJbKekozXaD5JBCLsfvRY7VBJi7jxBmzrg7j4tJPJO9S3GNDHbCV/ 15q9tkFNl1JCSfeS96hS4zBChuK6i0FBVCJGU16CvFpn2uBNE041X1Zz5Rb2mTMfTUOU 1uvQ== X-Received: by 10.60.83.116 with SMTP id p20mr34281053oey.83.1373610814327; Thu, 11 Jul 2013 23:33:34 -0700 (PDT) Received: from localhost ([202.108.130.138]) by mx.google.com with ESMTPSA id fk3sm53507667obb.2.2013.07.11.23.33.31 for (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Thu, 11 Jul 2013 23:33:33 -0700 (PDT) From: Liu Ping Fan To: qemu-devel@nongnu.org Date: Fri, 12 Jul 2013 14:32:51 +0800 Message-Id: <1373610771-11819-1-git-send-email-pingfank@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2607:f8b0:4003:c02::233 Cc: Paolo Bonzini Subject: [Qemu-devel] [PATCH] atomic: using memory_order_relaxed for refcnt inc/dec ops X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Refcnt's atomic inc/dec ops are frequent and its idiom need no seq_cst order. So to get better performance, it worth to adopt _relaxed other than _seq_cst memory model on them. We resort to gcc builtins. If gcc supports C11 memory model, __atomic_* buitlins is used, otherwise __sync_* builtins. Signed-off-by: Liu Ping Fan --- include/qemu/atomic.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index 0aa8913..1f474b7 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -183,8 +183,15 @@ #endif /* Provide shorter names for GCC atomic builtins. */ +#ifndef _GLIBCXX_ATOMIC_BUILTINS +/* close to C11 memory_order_seq_cst */ #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1) +#else +/* C11 memory_order_relaxed */ +#define atomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_RELAXED) +#define atomic_fetch_dec(ptr) __atomic_fetch_add(ptr, -1, __ATOMIC_RELAXED) +#endif #define atomic_fetch_add __sync_fetch_and_add #define atomic_fetch_sub __sync_fetch_and_sub #define atomic_fetch_and __sync_fetch_and_and @@ -192,8 +199,15 @@ #define atomic_cmpxchg __sync_val_compare_and_swap /* And even shorter names that return void. */ +#ifndef _GLIBCXX_ATOMIC_BUILTINS +/* close to C11 memory_order_seq_cst */ #define atomic_inc(ptr) ((void) __sync_fetch_and_add(ptr, 1)) #define atomic_dec(ptr) ((void) __sync_fetch_and_add(ptr, -1)) +#else +/* C11 memory_order_relaxed */ +#define atomic_inc(ptr) ((void) __atomic_fetch_add(ptr, 1, __ATOMIC_RELAXED)) +#define atomic_dec(ptr) ((void) __atomic_fetch_add(ptr, -1, __ATOMIC_RELAXED)) +#endif #define atomic_add(ptr, n) ((void) __sync_fetch_and_add(ptr, n)) #define atomic_sub(ptr, n) ((void) __sync_fetch_and_sub(ptr, n)) #define atomic_and(ptr, n) ((void) __sync_fetch_and_and(ptr, n))