From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 27 Jan 2016 01:57:38 +0100 (CET) Received: from e33.co.us.ibm.com ([32.97.110.151]:47236 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27010860AbcA0A5h30XeI (ORCPT ); Wed, 27 Jan 2016 01:57:37 +0100 Received: from localhost by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 26 Jan 2016 17:57:30 -0700 Received: from d03dlp03.boulder.ibm.com (9.17.202.179) by e33.co.us.ibm.com (192.168.1.133) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Tue, 26 Jan 2016 17:57:28 -0700 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-mips@linux-mips.org;ralf@linux-mips.org Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id A5BFE19D803E; Tue, 26 Jan 2016 17:45:27 -0700 (MST) Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u0R0vRnr29556738; Tue, 26 Jan 2016 17:57:27 -0700 Received: from d03av05.boulder.ibm.com (localhost [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u0R0vKRb031156; Tue, 26 Jan 2016 17:57:27 -0700 Received: from paulmck-ThinkPad-W541 (paulmck-thinkpad-w541.au.ibm.com [9.192.250.130]) by d03av05.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id u0R0vJii031119; Tue, 26 Jan 2016 17:57:19 -0700 Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id F04E316C11B1; Tue, 26 Jan 2016 16:57:30 -0800 (PST) Date: Tue, 26 Jan 2016 16:57:30 -0800 From: "Paul E. McKenney" To: Linus Torvalds Cc: Peter Zijlstra , Boqun Feng , Herbert Xu , Leonid Yegoshin , linux-mips , "linux-ia64@vger.kernel.org" , "Michael S. Tsirkin" , Will Deacon , virtualization , Peter Anvin , sparclinux@vger.kernel.org, Ingo Molnar , "linux-arch@vger.kernel.org" , linux-s390 , Russell King - ARM Linux , uml-devel , linux-sh@vger.kernel.org, Michael Ellerman , the arch/x86 maintainers , xen-devel@lists.xenproject.org, Ingo Molnar , linux-xtensa@linux-xtensa.org, James Hogan , Arnd Bergmann , Stefano Stabellini , adi-buildroot-devel@lists.sourceforge.net, David Daney , Thomas Gleixner , linux-metag@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" , Andrew Cooper , Linux Kernel Mailing List , Ralf Baechle , Joe Perches , ppc-dev , David Miller Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h Message-ID: <20160127005730.GE4503@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20160118081929.GA30420@gondor.apana.org.au> <20160118154629.GB3818@linux.vnet.ibm.com> <20160126165207.GB6029@fixme-laptop.cn.ibm.com> <20160126172227.GG6357@twins.programming.kicks-ass.net> <20160126201037.GU4503@linux.vnet.ibm.com> <20160126232921.GY4503@linux.vnet.ibm.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: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16012700-0009-0000-0000-000011C7A4E3 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 51449 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: paulmck@linux.vnet.ibm.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Tue, Jan 26, 2016 at 03:45:23PM -0800, Linus Torvalds wrote: > On Tue, Jan 26, 2016 at 3:29 PM, Paul E. McKenney > wrote: > > > > No trailing data-dependent read, so agreed, no smp_read_barrier_depends() > > needed. That said, I believe that we should encourage rcu_dereference*() > > or lockless_dereference() instead of READ_ONCE() for documentation > > reasons, though. > > I agree that that is likely the right thing to do in pretty much all situations. > > In theory, there might be performance situations where we'd want to > actively avoid the smp_read_barrier_depends() inherent in those, but > considering that it's only a performance issue on alpha, and we > probably have all of two or three people using Linux on alpha, it's a > pretty theoretical performance worry. Agreed! Thanx, Paul From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from e33.co.us.ibm.com ([32.97.110.151]:47236 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27010860AbcA0A5h30XeI (ORCPT ); Wed, 27 Jan 2016 01:57:37 +0100 Received: from localhost by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 26 Jan 2016 17:57:30 -0700 Date: Tue, 26 Jan 2016 16:57:30 -0800 From: "Paul E. McKenney" Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h Message-ID: <20160127005730.GE4503@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20160118081929.GA30420@gondor.apana.org.au> <20160118154629.GB3818@linux.vnet.ibm.com> <20160126165207.GB6029@fixme-laptop.cn.ibm.com> <20160126172227.GG6357@twins.programming.kicks-ass.net> <20160126201037.GU4503@linux.vnet.ibm.com> <20160126232921.GY4503@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Linus Torvalds Cc: Peter Zijlstra , Boqun Feng , Herbert Xu , Leonid Yegoshin , linux-mips , "linux-ia64@vger.kernel.org" , "Michael S. Tsirkin" , Will Deacon , virtualization , Peter Anvin , sparclinux@vger.kernel.org, Ingo Molnar , "linux-arch@vger.kernel.org" , linux-s390 , Russell King - ARM Linux , uml-devel , linux-sh@vger.kernel.org, Michael Ellerman , the arch/x86 maintainers , xen-devel@lists.xenproject.org, Ingo Molnar , linux-xtensa@linux-xtensa.org, James Hogan , Arnd Bergmann , Stefano Stabellini , adi-buildroot-devel@lists.sourceforge.net, David Daney , Thomas Gleixner , linux-metag@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" , Andrew Cooper , Linux Kernel Mailing List , Ralf Baechle , Joe Perches , ppc-dev , David Miller Message-ID: <20160127005730.EdR-g6x2e5MNtk2EdW5WG6vF7vRZA0Bp0CYsJqTf81I@z> On Tue, Jan 26, 2016 at 03:45:23PM -0800, Linus Torvalds wrote: > On Tue, Jan 26, 2016 at 3:29 PM, Paul E. McKenney > wrote: > > > > No trailing data-dependent read, so agreed, no smp_read_barrier_depends() > > needed. That said, I believe that we should encourage rcu_dereference*() > > or lockless_dereference() instead of READ_ONCE() for documentation > > reasons, though. > > I agree that that is likely the right thing to do in pretty much all situations. > > In theory, there might be performance situations where we'd want to > actively avoid the smp_read_barrier_depends() inherent in those, but > considering that it's only a performance issue on alpha, and we > probably have all of two or three people using Linux on alpha, it's a > pretty theoretical performance worry. Agreed! Thanx, Paul