From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751722AbeAYJfp (ORCPT ); Thu, 25 Jan 2018 04:35:45 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:41808 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751686AbeAYJfh (ORCPT ); Thu, 25 Jan 2018 04:35:37 -0500 Date: Thu, 25 Jan 2018 01:35:29 -0800 From: "Paul E. McKenney" To: Will Deacon Cc: stern@rowland.harvard.edu, parri.andrea@gmail.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, linux-kernel@vger.kernel.org, elena.reshetova@intel.com, mhocko@suse.com, linux-arch@vger.kernel.org Subject: Re: [PATCH v2] Automate memory-barriers.txt; provide Linux-kernel memory model Reply-To: paulmck@linux.vnet.ibm.com References: <20180119035855.GA29296@linux.vnet.ibm.com> <20180119171211.GA13636@linux.vnet.ibm.com> <20180124000014.GA1562@linux.vnet.ibm.com> <20180124105955.GA21491@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180124105955.GA21491@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18012509-0024-0000-0000-000003190FE1 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008423; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000247; SDB=6.00980077; UDB=6.00496807; IPR=6.00759378; BA=6.00005794; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00019199; XFM=3.00000015; UTC=2018-01-25 09:35:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18012509-0025-0000-0000-000046C2B5BB Message-Id: <20180125093529.GA3741@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-01-25_03:,, 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-1801250133 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 24, 2018 at 10:59:55AM +0000, Will Deacon wrote: > Hi Paul, > > On Tue, Jan 23, 2018 at 04:00:14PM -0800, Paul E. McKenney wrote: > > On Fri, Jan 19, 2018 at 09:12:11AM -0800, Paul E. McKenney wrote: > > > On Thu, Jan 18, 2018 at 07:58:55PM -0800, Paul E. McKenney wrote: > > > > Hello! > > > > > > > > There is some reason to believe that Documentation/memory-barriers.txt > > > > could use some help, and a major purpose of this patch is to provide > > > > that help in the form of a design-time tool that can produce all valid > > > > executions of a small fragment of concurrent Linux-kernel code, which is > > > > called a "litmus test". This tool's functionality is roughly similar to > > > > a full state-space search. Please note that this is a design-time tool, > > > > not useful for regression testing. However, we hope that the underlying > > > > Linux-kernel memory model will be incorporated into other tools capable > > > > of analyzing large bodies of code for regression-testing purposes. > > > > > > > > The main tool is herd7, together with the linux-kernel.bell, > > > > linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files > > > > added by this patch. The herd7 executable takes the other files as input, > > > > and all of these files collectively define the Linux-kernel memory memory > > > > model. A brief description of each of these other files is provided > > > > in the README file. Although this tool does have its limitations, > > > > which are documented in the README file, it does improve on the version > > > > reported on in the LWN series (https://lwn.net/Articles/718628/ and > > > > https://lwn.net/Articles/720550/) by supporting locking and arithmetic, > > > > including a much wider variety of read-modify-write atomic operations. > > > > Please note that herd7 is not part of this submission, but is freely > > > > available from http://diy.inria.fr/sources/index.html (and via "git" > > > > at https://github.com/herd/herdtools7). > > > > > > Please note that the latest version of herd is necessary for this version > > > of the memory model. With older versions, you will get error messages > > > like the following: > > > > > > File "./linux-kernel.def", line 44, characters 29-30: unexpected '-' (in macros) > > > > > > Many thanks to Andrea for spotting this one! > > > > And given that I am hearing no objections, I am thinking in terms of > > sending this in a pull request later this week. > > No objections from me. I can't claim to have deep knowledge about everything > being contributed here, but I think that the documentation is well-written > and a welcome addition to the codebase (thanks, Alan!). I also find that, > whilst complicated, the gist of the .cat file comes across pretty well and > is less confusing than the previous situation where we had two .cat files > for the strong and weak models. > > At this stage of maturity, I think that this is all much better as part of > the kernel sources and maintained as such, knowing that things will change > as we encounter new tests and CPU architectures. Sounds very good to me! I just sent a pull request. Wish me luck. ;-) Thanx, Paul