Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757061AbaFSB5q (ORCPT ); Wed, 18 Jun 2014 21:57:46 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:52568 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1754277AbaFSB5p (ORCPT ); Wed, 18 Jun 2014 21:57:45 -0400 X-IronPort-AV: E=Sophos;i="5.00,735,1396972800"; d="scan'208";a="32122520" Message-ID: <53A243B8.4010501@cn.fujitsu.com> Date: Thu, 19 Jun 2014 09:58:16 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: Tejun Heo CC: , , , "Paul E. McKenney" Subject: Re: [PATCH 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() References: <1403053685-28240-1-git-send-email-tj@kernel.org> <1403053685-28240-7-git-send-email-tj@kernel.org> <53A1097F.3060400@cn.fujitsu.com> <20140618153222.GA11042@htj.dyndns.org> In-Reply-To: <20140618153222.GA11042@htj.dyndns.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.103] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/2014 11:32 PM, Tejun Heo wrote: > On Wed, Jun 18, 2014 at 11:37:35AM +0800, Lai Jiangshan wrote: >>> @@ -97,7 +98,10 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) >>> static inline bool __pcpu_ref_alive(struct percpu_ref *ref, >>> unsigned __percpu **pcpu_countp) >>> { >>> - unsigned long pcpu_ptr = ACCESS_ONCE(ref->pcpu_count_ptr); >>> + unsigned long pcpu_ptr; >>> + >>> + /* paired with smp_store_release() in percpu_ref_reinit() */ >>> + pcpu_ptr = smp_load_acquire(&ref->pcpu_count_ptr); >> >> >> Does "smp_load_acquire()" hurts the performance of percpu_ref_get/put() >> in non-x86 system? > > It's equivalent to data dependency barrier. The only arch which needs > something more than barrier() is alpha. It isn't an issue. > But I searched from the source, smp_load_acquire() is just barrier() in x86, arm64, ia64, s390, sparc, but it includes memory barrier instruction in other archs. CC Paul. If smp_load_acquire() is sufficient lightweight, I would update the SRCU. Thanks, Lai -- 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/