From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751817AbdGZPqX (ORCPT ); Wed, 26 Jul 2017 11:46:23 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:44972 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605AbdGZPqW (ORCPT ); Wed, 26 Jul 2017 11:46:22 -0400 Date: Wed, 26 Jul 2017 08:46:15 -0700 From: "Paul E. McKenney" To: Will Deacon Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Reply-To: paulmck@linux.vnet.ibm.com References: <1500933497-12612-4-git-send-email-paulmck@linux.vnet.ibm.com> <20170725163318.bporqvcoodtel4a6@hirez.programming.kicks-ass.net> <20170725164900.GR3730@linux.vnet.ibm.com> <20170725165957.alykngbnrrwn3onw@hirez.programming.kicks-ass.net> <20170725171701.GS3730@linux.vnet.ibm.com> <20170725185320.uis4hxqaqlx7y7gp@hirez.programming.kicks-ass.net> <20170725193612.GW3730@linux.vnet.ibm.com> <20170725202451.GC28975@worktop> <20170725211926.GA3730@linux.vnet.ibm.com> <20170726093645.GA2115@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170726093645.GA2115@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17072615-0048-0000-0000-000001C9F07B X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007429; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00893213; UDB=6.00446526; IPR=6.00673377; BA=6.00005492; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016390; XFM=3.00000015; UTC=2017-07-26 15:46:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072615-0049-0000-0000-00004204C0F0 Message-Id: <20170726154615.GP3730@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-26_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=3 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707260227 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 26, 2017 at 10:36:46AM +0100, Will Deacon wrote: > On Tue, Jul 25, 2017 at 02:19:26PM -0700, Paul E. McKenney wrote: > > Some architectures are less precise than others in tracking which > > CPUs are running a given process due to ASIDs, though this is > > thought to be a non-problem: > > > > https://marc.info/?l=linux-arch&m=126716090413065&w=2 > > https://marc.info/?l=linux-arch&m=126716262815202&w=2 > > > > Thoughts? > > On arm64, we *never* touch mm_cpumask, so it will always be empty. The only > thing we could potentially use it for is non-broadcast TLB invalidation if > the mm was only active on a single CPU, but when I implemented that we > pretty much never hit that case. I was hoping fork()+exec() would trigger it > (e.g. scripts), but the scheduler treats both of those as rebalancing points > so the temporary ASID before the exec always has two CPUs set in its mask. OK, so it sounds like we should ignore ->mm_cpumask except possibly for an architecture-specific optimization, and rely solely on ->mm in the absence of such optimizations, right? Thanx, Paul