From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751832AbdGYQti (ORCPT ); Tue, 25 Jul 2017 12:49:38 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:49521 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751788AbdGYQtg (ORCPT ); Tue, 25 Jul 2017 12:49:36 -0400 Date: Tue, 25 Jul 2017 09:49:00 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170725163318.bporqvcoodtel4a6@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17072516-0040-0000-0000-00000385800E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007424; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00892754; UDB=6.00446251; IPR=6.00672918; 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=3.00016372; XFM=3.00000015; UTC=2017-07-25 16:49:04 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17072516-0041-0000-0000-000007799E18 Message-Id: <20170725164900.GR3730@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-25_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-1707250265 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 25, 2017 at 06:33:18PM +0200, Peter Zijlstra wrote: > On Mon, Jul 24, 2017 at 02:58:16PM -0700, Paul E. McKenney wrote: > > The sys_membarrier() system call has proven too slow for some use > > cases, which has prompted users to instead rely on TLB shootdown. > > Although TLB shootdown is much faster, it has the slight disadvantage > > of not working at all on arm and arm64. This commit therefore adds > > an expedited option to the sys_membarrier() system call. > > > @@ -64,6 +65,10 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) > > if (num_online_cpus() > 1) > > synchronize_sched(); > > return 0; > > + case MEMBARRIER_CMD_SHARED_EXPEDITED: > > + if (num_online_cpus() > 1) > > + synchronize_sched_expedited(); > > + return 0; > > So you now give unprivileged userspace the means to IPI the entire > machine? > > So what do we do when someone goes and does: > > for (;;) > sys_membarrier(MEMBARRIER_CMD_SHARED_EXPEDITED, 0); > > on us? The same thing that happens when they call munmap(). Thanx, Paul