From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641AbdG0M5s (ORCPT ); Thu, 27 Jul 2017 08:57:48 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:47254 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751466AbdG0M5r (ORCPT ); Thu, 27 Jul 2017 08:57:47 -0400 Date: Thu, 27 Jul 2017 05:56:59 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: 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: <20170724215758.GA12075@linux.vnet.ibm.com> <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> <20170727101426.gvbympkitoqyvfxj@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170727101426.gvbympkitoqyvfxj@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17072712-2213-0000-0000-00000200801A X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007435; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00893636; UDB=6.00446780; IPR=6.00673797; BA=6.00005494; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016408; XFM=3.00000015; UTC=2017-07-27 12:57:03 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072712-2214-0000-0000-00005704710C Message-Id: <20170727125659.GO3730@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-27_06:,, 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-1707270203 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 27, 2017 at 12:14:26PM +0200, Peter Zijlstra wrote: > On Tue, Jul 25, 2017 at 12:36:12PM -0700, Paul E. McKenney wrote: > > This horse is already out, so trying to shut the gate won't be effective. > > So I'm not convinced it is. The mprotect() hack isn't portable as we've > established and on x86 where it does work, it doesn't (much) perturb > tasks not related to our process because we keep a tight mm_cpumask(). Wrong. People are using it today, portable or not. If we want them to stop using it, we need to give them an alternative. Period. > And if there are other (unpriv.) means of spraying IPIs around, we > should most certainly look at fixing those, not just shrug and make > matters worse. We need to keep an open mind for a bit. If there was a trivial solution, we would have implemented it back in 2010. Thanx, Paul