From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757011AbeDBTb1 (ORCPT ); Mon, 2 Apr 2018 15:31:27 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:50892 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754396AbeDBTb0 (ORCPT ); Mon, 2 Apr 2018 15:31:26 -0400 Date: Mon, 2 Apr 2018 12:31:54 -0700 From: "Paul E. McKenney" To: Alan Stern Cc: schwidefsky@de.ibm.com, borntraeger@de.ibm.com, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, parri.andrea@gmail.com, will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com Subject: Re: [PATCH RFC tools/memory-model] Add s390.{cfg,cat} Reply-To: paulmck@linux.vnet.ibm.com References: <20180329021812.GV3675@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-GCONF: 00 x-cbid: 18040219-0036-0000-0000-000002DAB100 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008790; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000255; SDB=6.01012159; UDB=6.00515827; IPR=6.00791429; MB=3.00020378; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-02 19:31:02 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040219-0037-0000-0000-000043D81E11 Message-Id: <20180402193154.GA3948@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-04-02_08:,, 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-1804020212 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 29, 2018 at 10:40:43AM -0400, Alan Stern wrote: > On Wed, 28 Mar 2018, Paul E. McKenney wrote: > > > > > In the meantime, does the cat file look to you like it correctly > > > > models the combination of TSO and multicopy atomicity? Do the > > > > fences really work, or did I just get lucky with my choice of > > > > litmus tests? > > > > > > You got lucky. Try creating an SB litmus test where, instead of an > > > smp_mb() fence between the write and the read, each thread executes > > > some other kind of fence. > > > > Ah, it does indeed get "Never" in that case, which I do not believe > > to e correct. > > > > > The acyclicity condition should have been written more like this: > > > > > > let po_ghb = ([R] ; po ; [M]) | ([M] ; po ; [W]) > > > > > > acyclic mfence | po_ghb | rf | fr | co as tso-mca > > > > > > I don't know what the fence instruction is on s390; change the "mfence" > > > above accordingly. The main difference between this and the > > > corresponding expression in x86tso.cat is that I replaced rfe with rf. > > > > The s390 fence instruction is "bcr 14,0" or "bcr 15,0", depending on > > how recent of hardware you are running. The latter works everywhere, > > if I recall correctly. But I do not believe that herd knows about either > > instruction yet. > > Herd does not need to understand s390 assembly in order to handle the > things defined in linux.def, such as "smp_mb()". linux.def doesn't > contain any x86 assembly language stuff either (or PPC or ARM). > > > Ah, and I need to lose the "empty rmw & (fre;coe)". > > That appears to be where my spurious ordering was coming from, strange > > though that seems to me. > > No, don't drop it; it was not the source of your spurious ordering. > The extra ordering came from your "(po \ (W * R))" term, which > unintentionally matches fences as well as memory accesses. > > > And your use of "rf" instead of "rfe" makes sense, as that is what makes > > the read-from-write provide ordering, correct? And that should also cover > > the "Uniproc check" that would otherwise be required, right? > > I don't think so... > > > Except that I get "Sometimes" on CoWR+poonceonce+Once.litmus... > > Exactly. > > > Which I can fix by unioning po-loc into po-ghb. Or is there some > > better way to do this? > > You could just keep the "uniproc" check. These two approaches accept > the same set of litmus tests. > > Logically, I think of these as two distinct categories of ordering. > po_ghb and tso-mca have to do with the order in which stores reach the > cache, whereas "uniproc" (AKA sequential consistency per variable) has > to do with enforcement of the cache coherence requirements. Clearly > they are related, but they aren't the same thing. > > > > This doesn't account for atomic operations properly; see the "implied" > > > term in x86tso.cat. > > > > I will look at this more later, reaching end of both battery and useful > > attention span... Like the following, perhaps? Thanx, Paul ------------------------------------------------------------------------ s390 include "fences.cat" include "cos.cat" (* Fundamental coherence ordering *) let com = rf | co | fr acyclic po-loc | com as coherence (* Atomic *) empty rmw & (fre;coe) as atom (* Fences *) let mb = [M] ; fencerel(Mb) ; [M] (* TSO with multicopy atomicity *) let po-ghb = ([R] ; po ; [M]) | ([M] ; po ; [W]) acyclic mb | po-ghb | fr | rf | co as sc