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McKenney" To: Alan Stern Cc: Will Deacon , LKMM Maintainers -- Akira Yokosawa , Andrea Parri , Boqun Feng , David Howells , Jade Alglave , Luc Maranget , Nicholas Piggin , Peter Zijlstra , Kernel development list Subject: Re: [PATCH 2/2] tools/memory-model: Add write ordering by release-acquire and by locks Reply-To: paulmck@linux.vnet.ibm.com References: <20180622183007.GD1802@arm.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: 18062220-0068-0000-0000-0000030CFC19 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009242; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000265; SDB=6.01050833; UDB=6.00538564; IPR=6.00829803; MB=3.00021811; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-22 20:51:25 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062220-0069-0000-0000-000044C6A771 Message-Id: <20180622205324.GU3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-22_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 mlxscore=0 impostorscore=0 mlxlogscore=896 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806220230 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 03:11:37PM -0400, Alan Stern wrote: > On Fri, 22 Jun 2018, Will Deacon wrote: > > On Fri, Jun 22, 2018 at 02:09:04PM -0400, Alan Stern wrote: [ . . . ] > > > > Could we drop the acquire/release stuff from the patch and limit this change > > > > to locking instead? > > > > > > The LKMM uses the same CAT code for acquire/release and lock/unlock. > > > (In essence, it considers a lock to be an acquire and an unlock to be a > > > release; everything else follows from that.) Treating one differently > > > from the other in these tests would require some significant changes. > > > It wouldn't be easy. > > > > It would be boring if it was easy ;) I think this is a case of the tail > > wagging the dog. > > > > Paul -- please can you drop this patch until we've resolved this discussion? > > Agreed. It sounds like we'll need two versions of the Rel and Acq sets > in the memory model; one for RCpc and one for RCsc. smp_load_acquire > and smp_store_release will use the former, and locking will use the > latter. Done! Thanx, Paul > Would it suffice to have this duplication just for release, using a > single version of acquire? What would happen on ARMv8 or RISC-V if an > RCsc release was read by an RCpc acquire? Or vice versa? > > Alan >