From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753220Ab3J3J1f (ORCPT ); Wed, 30 Oct 2013 05:27:35 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:58024 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751332Ab3J3J1e (ORCPT ); Wed, 30 Oct 2013 05:27:34 -0400 Date: Wed, 30 Oct 2013 02:27:25 -0700 From: "Paul E. McKenney" To: Victor Kaplansky Cc: Oleg Nesterov , Anton Blanchard , Benjamin Herrenschmidt , Frederic Weisbecker , LKML , Linux PPC dev , Mathieu Desnoyers , Michael Ellerman , Michael Neuling , Peter Zijlstra Subject: Re: perf events ring buffer memory barrier on powerpc Message-ID: <20131030092725.GL4126@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <12083.1382486094@ale.ozlabs.ibm.com> <20131023141948.GB3566@localhost.localdomain> <20131025173749.GG19466@laptop.lan> <20131028132634.GO19466@laptop.lan> <20131028163418.GD4126@linux.vnet.ibm.com> <20131028201735.GA15629@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13103009-9332-0000-0000-000001F955DD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 28, 2013 at 10:58:58PM +0200, Victor Kaplansky wrote: > Oleg Nesterov wrote on 10/28/2013 10:17:35 PM: > > > mb(); // XXXXXXXX: do we really need it? I think yes. > > Oh, it is hard to argue with feelings. Also, it is easy to be on > conservative side and put the barrier here just in case. > But I still insist that the barrier is redundant in your example. If you were to back up that insistence with a description of the orderings you are relying on, why other orderings are not important, and how the important orderings are enforced, I might be tempted to pay attention to your opinion. Thanx, Paul From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e34.co.us.ibm.com (e34.co.us.ibm.com [32.97.110.152]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e34.co.us.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 46D8A2C0366 for ; Wed, 30 Oct 2013 20:27:33 +1100 (EST) Received: from /spool/local by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 30 Oct 2013 03:27:31 -0600 Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 3FEE61FF001B for ; Wed, 30 Oct 2013 03:27:15 -0600 (MDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r9U9RSM4188820 for ; Wed, 30 Oct 2013 03:27:28 -0600 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r9U9UH99000308 for ; Wed, 30 Oct 2013 03:30:18 -0600 Date: Wed, 30 Oct 2013 02:27:25 -0700 From: "Paul E. McKenney" To: Victor Kaplansky Subject: Re: perf events ring buffer memory barrier on powerpc Message-ID: <20131030092725.GL4126@linux.vnet.ibm.com> References: <12083.1382486094@ale.ozlabs.ibm.com> <20131023141948.GB3566@localhost.localdomain> <20131025173749.GG19466@laptop.lan> <20131028132634.GO19466@laptop.lan> <20131028163418.GD4126@linux.vnet.ibm.com> <20131028201735.GA15629@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: Michael Neuling , Mathieu Desnoyers , Peter Zijlstra , Oleg Nesterov , LKML , Linux PPC dev , Anton Blanchard , Frederic Weisbecker Reply-To: paulmck@linux.vnet.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Oct 28, 2013 at 10:58:58PM +0200, Victor Kaplansky wrote: > Oleg Nesterov wrote on 10/28/2013 10:17:35 PM: > > > mb(); // XXXXXXXX: do we really need it? I think yes. > > Oh, it is hard to argue with feelings. Also, it is easy to be on > conservative side and put the barrier here just in case. > But I still insist that the barrier is redundant in your example. If you were to back up that insistence with a description of the orderings you are relying on, why other orderings are not important, and how the important orderings are enforced, I might be tempted to pay attention to your opinion. Thanx, Paul