From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751411AbcGMWc4 (ORCPT ); Wed, 13 Jul 2016 18:32:56 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34299 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbcGMWcs (ORCPT ); Wed, 13 Jul 2016 18:32:48 -0400 X-IBM-Helo: d03dlp01.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Wed, 13 Jul 2016 15:33:02 -0700 From: "Paul E. McKenney" To: Tejun Heo Cc: Peter Zijlstra , John Stultz , Ingo Molnar , lkml , Dmitry Shmidt , Rom Lemarchand , Colin Cross , Todd Kjos , Oleg Nesterov Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes Reply-To: paulmck@linux.vnet.ibm.com References: <20160713183347.GK4065@mtj.duckdns.org> <20160713201823.GB29670@mtj.duckdns.org> <20160713202657.GW30154@twins.programming.kicks-ass.net> <20160713203944.GC29670@mtj.duckdns.org> <20160713205102.GZ30909@twins.programming.kicks-ass.net> <20160713210315.GO7094@linux.vnet.ibm.com> <20160713210526.GF29670@mtj.duckdns.org> <20160713211841.GQ7094@linux.vnet.ibm.com> <20160713220128.GA15005@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160713220128.GA15005@htj.duckdns.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16071322-0012-0000-0000-00001028ABD0 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16071322-0013-0000-0000-000043A0E82D Message-Id: <20160713223302.GT7094@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-13_12:,, 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=8.0.1-1604210000 definitions=main-1607130246 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2016 at 06:01:28PM -0400, Tejun Heo wrote: > Hello, Paul. > > On Wed, Jul 13, 2016 at 02:18:41PM -0700, Paul E. McKenney wrote: > > On Wed, Jul 13, 2016 at 05:05:26PM -0400, Tejun Heo wrote: > > > On Wed, Jul 13, 2016 at 02:03:15PM -0700, Paul E. McKenney wrote: > > > > Take the patch that I just sent out and make the choice of normal > > > > vs. expedited depend on CONFIG_PREEMPT_RT or whatever the -rt guys are > > > > calling it these days. Is there a low-latency Kconfig option other > > > > than CONFIG_NO_HZ_FULL? > > > > > > Sounds like a plan to me. > > > > I like the way we like each other's idea. Mutually assured laziness? ;-) > > Heh, indeed. :) > > Technically, I think the lglock approach would be better here given > the combination of requirements; however, it's quite a bit more code > which would likely require some sophistications down the line (like > blocking new readers first at the start of down_write). If we have to > go there, we'll go there but for now I think it'd be simpler to > conditionally switch to the expedited operations. It can be a config > option which is selected by !RT as you suggested. If anyone hits an > actual issue with that, we can go for the lglock thing. Fair enough! ;-) Thanx, Paul