From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751708AbdGZPmh (ORCPT ); Wed, 26 Jul 2017 11:42:37 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45908 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751379AbdGZPmf (ORCPT ); Wed, 26 Jul 2017 11:42:35 -0400 Date: Wed, 26 Jul 2017 08:42:29 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Mathieu Desnoyers , linux-kernel , Ingo Molnar , Lai Jiangshan , dipankar , Andrew Morton , Josh Triplett , Thomas Gleixner , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , Will Deacon Subject: Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Reply-To: paulmck@linux.vnet.ibm.com References: <20170724215758.GA12075@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> <20170725215510.GD28975@worktop> <1480480872.25829.1501023013862.JavaMail.zimbra@efficios.com> <20170726074656.obadfdu6hdlrmy7r@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170726074656.obadfdu6hdlrmy7r@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17072615-0008-0000-0000-00000264E8C9 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007429; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00893211; UDB=6.00446525; IPR=6.00673375; 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 15:42:32 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072615-0009-0000-0000-000036298653 Message-Id: <20170726154229.GO3730@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=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1707260226 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 26, 2017 at 09:46:56AM +0200, Peter Zijlstra wrote: > On Tue, Jul 25, 2017 at 10:50:13PM +0000, Mathieu Desnoyers wrote: > > This would implement a MEMBARRIER_CMD_PRIVATE_EXPEDITED (or such) flag > > for expedited process-local effect. This differs from the "SHARED" flag, > > since the SHARED flag affects threads accessing memory mappings shared > > across processes as well. > > > > I wonder if we could create a MEMBARRIER_CMD_SHARED_EXPEDITED behavior > > by iterating on all memory mappings mapped into the current process, > > and build a cpumask based on the union of all mm masks encountered ? > > Then we could send the IPI to all cpus belonging to that cpumask. Or > > am I missing something obvious ? > > I would readily object to such a beast. You far too quickly end up > having to IPI everybody because of some stupid shared map or something > (yes I know, normal DSOs are mapped private). Agreed, we should keep things simple to start with. The user can always invoke sys_membarrier() from each process. Thanx, Paul > The whole private_expedited is only palatable because we can only hinder > our own threads (much). >