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McKenney" To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org Cc: stern@rowland.harvard.edu, 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: Q&A from "Concurrency with tools/memory-model" Reply-To: paulmck@linux.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18111522-0040-0000-0000-0000049333FE X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010057; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000270; SDB=6.01117993; UDB=6.00577119; IPR=6.00898102; MB=3.00024184; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-15 22:56:35 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18111522-0041-0000-0000-0000089C3FE6 Message-Id: <20181115225630.GA30917@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-15_17:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=343 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1811150198 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! Good turnout and some good questions here in Vancouver BC, please see below for rough notes. ;-) Thanx, Paul ------------------------------------------------------------------------ "Concurrency with tools/memory-model" Andrea Parri presenting. Rough notes of Q&A. o Want atomic bit operation. o But smp_read_barrier_depends() not there, so how to note pairing? A: Note the dependency as the other end of the pairing. o Speculation barriers, as in Spectre and Meltdown? A: This would require adding timing, not in the immediate future. o What ordering does system calls provide? A: None that we know of. Boqun: Userspace needs to explicitly provide the needed ordering when interacting with the kernel. Some architectures do provide full barriers, but not to be counted on. o Why herd7? A: Based on other formalizations -- note that herd7 had a number of hardware models. Paul: Plus the founder of the LKMM project is a co-author of herd, which might have had some effect. o Why not also model interrupts and NMIs? Promela and spin have been used for this. A: Cannot currently model them. You can emulated them with additional threads and locks, if you wish. Vincent Nimal and Lihao Liang have done some academic work on these topics.