From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966653AbcKLR61 (ORCPT ); Sat, 12 Nov 2016 12:58:27 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:33467 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756786AbcKLR6Z (ORCPT ); Sat, 12 Nov 2016 12:58:25 -0500 Date: Sat, 12 Nov 2016 09:58:20 -0800 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: linux-kernel , Josh Triplett , rostedt , Lai Jiangshan , stable Subject: Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Reply-To: paulmck@linux.vnet.ibm.com References: <1478190568-5829-1-git-send-email-mathieu.desnoyers@efficios.com> <20161103174911.GL3716@linux.vnet.ibm.com> <656710430.17218.1478538539895.JavaMail.zimbra@efficios.com> <20161107180614.GR24166@linux.vnet.ibm.com> <1462452244.17824.1478542214440.JavaMail.zimbra@efficios.com> <20161107200315.GA3438@linux.vnet.ibm.com> <26153082.18614.1478603751607.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <26153082.18614.1478603751607.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111217-0016-0000-0000-00000528E026 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006065; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00779910; UDB=6.00375910; IPR=6.00557296; BA=6.00004873; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013305; XFM=3.00000011; UTC=2016-11-12 17:58:22 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111217-0017-0000-0000-000034980AA5 Message-Id: <20161112175820.GV4127@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-12_05:,, 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=8.0.1-1609300000 definitions=main-1611120326 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 08, 2016 at 11:15:51AM +0000, Mathieu Desnoyers wrote: > ----- On Nov 7, 2016, at 3:03 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote: > > > On Mon, Nov 07, 2016 at 06:10:14PM +0000, Mathieu Desnoyers wrote: > >> > >> ----- On Nov 7, 2016, at 1:06 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com > >> wrote: > >> > >> > On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote: > >> >> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com > >> >> wrote: > >> >> > >> >> > On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote: > >> >> >> Userspace applications should be allowed to expect the membarrier system > >> >> >> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on > >> >> >> nohz_full CPUs, but synchronize_sched() does not take those into > >> >> >> account. > >> >> >> > >> >> >> Given that we do not want unrelated processes to be able to affect > >> >> >> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier > >> >> >> is invoked on a kernel with enabled nohz_full CPUs. > >> >> >> > >> >> >> Signed-off-by: Mathieu Desnoyers > >> >> >> CC: "Paul E. McKenney" > >> >> > > >> >> > Acked-by: "Paul E. McKenney" > >> >> > >> >> Hi Paul, > >> >> > >> >> Do you plan to pick it up through your tree, or I should sent > >> >> it directly to Linus ? > >> > > >> > Your choice. I believe that the original went some other way, but I > >> > would be fine carrying this one. > >> > >> Not sure what you mean by "the original" ? And which other way ? > >> I have not been notified about this. > > > > If I remember correctly, you sent the original sys_membarrier() > > patch through akpm or similar. > > Ah right, the original implementation, yes. > > > > >> If you can carry this patch it would be very much appreciated, > > > > Will do! > > Especially since the regression is somewhat related to RCU > behavior wrt nohz_full, getting it through your tree seems > relevant. I have it queued for 4.11, thank you! Thanx, Paul