From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks Date: Tue, 26 Jan 2016 13:37:38 -0800 Message-ID: <56A7E722.7030701@zytor.com> References: <1452635935-5439-1-git-send-email-mst@redhat.com> <56957D54.5000602@zytor.com> <20160126101921-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160126101921-mutt-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: Davidlohr Bueso , Davidlohr Bueso , Peter Zijlstra , the arch/x86 maintainers , linux-kernel@vger.kernel.org, virtualization , Borislav Petkov , Thomas Gleixner , "Paul E. McKenney" , Linus Torvalds , Ingo Molnar List-Id: virtualization@lists.linuxfoundation.org On 01/26/16 00:20, Michael S. Tsirkin wrote: > On Tue, Jan 12, 2016 at 02:25:24PM -0800, H. Peter Anvin wrote: > > Hi hpa, > Any luck getting some feedback on this one? > Yes. What we know so far is that *most* cases it will work, but there are apparently a few corner cases where MFENCE or a full-blown serializing instruction is necessary. We are trying to characterize those corner cases and see if any of them affect the kernel. Even if they are, we can probably make those barriers explicitly different, but we don't want to go ahead with the change until we know where we need to care. -hpa From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752044AbcAZVi7 (ORCPT ); Tue, 26 Jan 2016 16:38:59 -0500 Received: from terminus.zytor.com ([198.137.202.10]:55546 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054AbcAZViz (ORCPT ); Tue, 26 Jan 2016 16:38:55 -0500 Subject: Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks To: "Michael S. Tsirkin" References: <1452635935-5439-1-git-send-email-mst@redhat.com> <56957D54.5000602@zytor.com> <20160126101921-mutt-send-email-mst@redhat.com> Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Davidlohr Bueso , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "Paul E. McKenney" , the arch/x86 maintainers , Davidlohr Bueso , virtualization , Borislav Petkov From: "H. Peter Anvin" Message-ID: <56A7E722.7030701@zytor.com> Date: Tue, 26 Jan 2016 13:37:38 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <20160126101921-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/26/16 00:20, Michael S. Tsirkin wrote: > On Tue, Jan 12, 2016 at 02:25:24PM -0800, H. Peter Anvin wrote: > > Hi hpa, > Any luck getting some feedback on this one? > Yes. What we know so far is that *most* cases it will work, but there are apparently a few corner cases where MFENCE or a full-blown serializing instruction is necessary. We are trying to characterize those corner cases and see if any of them affect the kernel. Even if they are, we can probably make those barriers explicitly different, but we don't want to go ahead with the change until we know where we need to care. -hpa