From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760298AbdKPSCS (ORCPT ); Thu, 16 Nov 2017 13:02:18 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50908 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936391AbdKPRsi (ORCPT ); Thu, 16 Nov 2017 12:48:38 -0500 Date: Thu, 16 Nov 2017 09:48:30 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Nick Desaulniers , Sami Tolvanen , Will Deacon , Alex Matveev , Andi Kleen , Ard Biesheuvel , Greg Hackmann , Kees Cook , linux-arm-kernel@lists.infradead.org, Linux Kbuild mailing list , LKML , Mark Rutland , Masahiro Yamada , Maxim Kuvyrkov , Michal Marek , Yury Norov , Matthias Kaehlcke Subject: Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG Reply-To: paulmck@linux.vnet.ibm.com References: <20171115213428.22559-1-samitolvanen@google.com> <20171115213428.22559-19-samitolvanen@google.com> <20171116115810.GH9361@arm.com> <20171116161731.GA94341@samitolvanen.mtv.corp.google.com> <20171116163054.kcsdsomr7u2mqql2@hirez.programming.kicks-ass.net> <20171116165922.llrojrvomuihabrt@hirez.programming.kicks-ass.net> <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17111617-0008-0000-0000-000002A22C11 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008075; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000240; SDB=6.00946792; UDB=6.00477950; IPR=6.00727083; BA=6.00005695; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018048; XFM=3.00000015; UTC=2017-11-16 17:48:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17111617-0009-0000-0000-000037545FBE Message-Id: <20171116174830.GX3624@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-16_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1711160237 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 16, 2017 at 06:34:17PM +0100, Peter Zijlstra wrote: > On Thu, Nov 16, 2017 at 09:16:49AM -0800, Nick Desaulniers wrote: > > On Thu, Nov 16, 2017 at 8:59 AM, Peter Zijlstra wrote: > > > On Thu, Nov 16, 2017 at 08:50:41AM -0800, Nick Desaulniers wrote: > > >> On Thu, Nov 16, 2017 at 8:30 AM, Peter Zijlstra wrote: > > >> > > >> > Ideally we'd get the toolchain people to commit to supporting the kernel > > >> > memory model along side the C11 one. That would help a ton. > > >> > > >> Does anyone from the kernel side participate in the C standardization process? > > > > > > Yes, Paul McKenney and Will Deacon. Doesn't mean these two can still be > > > reconciled though. From what I understand C11 (and onwards) are > > > incompatible with the kernel model on a number of subtle points. > > > > It would be good to have these incompatibilities written down, then > > for the sake of argument, they can be cited both for discussions on > > LKML and in the C standardization process. For example, a running > > list in Documentation/ or something would make it so that anyone could > > understand and cite current issues with the latest C standard. > > Will should be able to produce this list; I know he's done before, I > just can't find it -- my Google-foo isn't strong today. Here you go: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0124r4.html > > I don't understand why we'd block patches for enabling experimental > > features. We've been running this patch-set on actual devices for > > months and would love to provide them to the community for further > > testing. If bugs are found, then there's more evidence to bring to > > the C standards committee. Otherwise we're shutting down feature > > development for the sake of potential bugs in a C standard we're not > > even using. > > So the problem is that its very very hard (and painful) to find these > bugs. Getting the tools people to comment on these specific > optimizations would really help lots. It would be good to get something similar to LKMM into KTSAN, for example. There would probably be a few differences due to efficiency concerns, but closer is better than less close. ;-) Thanx, Paul From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@linux.vnet.ibm.com (Paul E. McKenney) Date: Thu, 16 Nov 2017 09:48:30 -0800 Subject: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG In-Reply-To: <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> References: <20171115213428.22559-1-samitolvanen@google.com> <20171115213428.22559-19-samitolvanen@google.com> <20171116115810.GH9361@arm.com> <20171116161731.GA94341@samitolvanen.mtv.corp.google.com> <20171116163054.kcsdsomr7u2mqql2@hirez.programming.kicks-ass.net> <20171116165922.llrojrvomuihabrt@hirez.programming.kicks-ass.net> <20171116173417.nqsh5dpu65uj7b5s@hirez.programming.kicks-ass.net> Message-ID: <20171116174830.GX3624@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Nov 16, 2017 at 06:34:17PM +0100, Peter Zijlstra wrote: > On Thu, Nov 16, 2017 at 09:16:49AM -0800, Nick Desaulniers wrote: > > On Thu, Nov 16, 2017 at 8:59 AM, Peter Zijlstra wrote: > > > On Thu, Nov 16, 2017 at 08:50:41AM -0800, Nick Desaulniers wrote: > > >> On Thu, Nov 16, 2017 at 8:30 AM, Peter Zijlstra wrote: > > >> > > >> > Ideally we'd get the toolchain people to commit to supporting the kernel > > >> > memory model along side the C11 one. That would help a ton. > > >> > > >> Does anyone from the kernel side participate in the C standardization process? > > > > > > Yes, Paul McKenney and Will Deacon. Doesn't mean these two can still be > > > reconciled though. From what I understand C11 (and onwards) are > > > incompatible with the kernel model on a number of subtle points. > > > > It would be good to have these incompatibilities written down, then > > for the sake of argument, they can be cited both for discussions on > > LKML and in the C standardization process. For example, a running > > list in Documentation/ or something would make it so that anyone could > > understand and cite current issues with the latest C standard. > > Will should be able to produce this list; I know he's done before, I > just can't find it -- my Google-foo isn't strong today. Here you go: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0124r4.html > > I don't understand why we'd block patches for enabling experimental > > features. We've been running this patch-set on actual devices for > > months and would love to provide them to the community for further > > testing. If bugs are found, then there's more evidence to bring to > > the C standards committee. Otherwise we're shutting down feature > > development for the sake of potential bugs in a C standard we're not > > even using. > > So the problem is that its very very hard (and painful) to find these > bugs. Getting the tools people to comment on these specific > optimizations would really help lots. It would be good to get something similar to LKMM into KTSAN, for example. There would probably be a few differences due to efficiency concerns, but closer is better than less close. ;-) Thanx, Paul