From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755095AbeDWNLX (ORCPT ); Mon, 23 Apr 2018 09:11:23 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:41944 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754874AbeDWNLV (ORCPT ); Mon, 23 Apr 2018 09:11:21 -0400 Date: Mon, 23 Apr 2018 06:12:28 -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, joel.opensrc@gmail.com Subject: Re: [PATCH tip/core/rcu 06/22] rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() Reply-To: paulmck@linux.vnet.ibm.com References: <20180423023150.GA21533@linux.vnet.ibm.com> <1524450747-22778-6-git-send-email-paulmck@linux.vnet.ibm.com> <20180423085347.GS4064@hirez.programming.kicks-ass.net> <20180423123223.GK26088@linux.vnet.ibm.com> <20180423124855.GZ4064@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180423124855.GZ4064@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18042313-0024-0000-0000-0000034CF5DB X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008905; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000257; SDB=6.01022101; UDB=6.00521662; IPR=6.00801336; MB=3.00020725; MTD=3.00000008; XFM=3.00000015; UTC=2018-04-23 13:11:18 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042313-0025-0000-0000-000047C41944 Message-Id: <20180423131227.GM26088@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-23_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804230137 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 23, 2018 at 02:48:55PM +0200, Peter Zijlstra wrote: > On Mon, Apr 23, 2018 at 05:32:23AM -0700, Paul E. McKenney wrote: > > On Mon, Apr 23, 2018 at 10:53:47AM +0200, Peter Zijlstra wrote: > > > On Sun, Apr 22, 2018 at 07:32:11PM -0700, Paul E. McKenney wrote: > > > > Commit e31d28b6ab8f ("trace: Eliminate cond_resched_rcu_qs() in favor > > > > of cond_resched()") substituted cond_resched() for the earlier call > > > > to cond_resched_rcu_qs(). However, the new-age cond_resched() does > > > > not do anything to help RCU-tasks grace periods because (1) RCU-tasks > > > > is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a > > > > complete no-op when preemption is enabled. This situation results > > > > in hangs when running the trace benchmarks. > > > > > > But a few patches earlier you tried to address that.. > > > > Yes. And all this patch does is change the name to better match > > what this primitive actually does. > > > > I could merge the two patches, if that would help. > > I understood the earlier patch was actually changing cond_resched() to > also work for task-rcu; which resulted in it acually not being a no-op > for PREEMPT anymore. > > But then here you say it doesn't because it's a no-op. > > It's not about the rename.. It is about one patch changing PREEMPT > cond_resched to not be a no-op and you here justifying things because > PREEMPT cond_resched it a no-op. So would it help if I instead said in the commit log that it is a no-op in production builds of the Linux kernel? Thanx, Paul