From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752301AbdHHSCO (ORCPT ); Tue, 8 Aug 2017 14:02:14 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57680 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752154AbdHHSCN (ORCPT ); Tue, 8 Aug 2017 14:02:13 -0400 Date: Tue, 8 Aug 2017 11:02:08 -0700 From: "Paul E. McKenney" To: Neeraj Upadhyay Cc: josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set Reply-To: paulmck@linux.vnet.ibm.com References: <1502212826-18846-1-git-send-email-neeraju@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1502212826-18846-1-git-send-email-neeraju@codeaurora.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17080818-0048-0000-0000-000001D07A84 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007508; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000217; SDB=6.00899434; UDB=6.00450196; IPR=6.00679639; BA=6.00005519; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016598; XFM=3.00000015; UTC=2017-08-08 18:02:10 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17080818-0049-0000-0000-0000422A0C4A Message-Id: <20170808180208.GF3730@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-08_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-1708080293 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 08, 2017 at 10:50:26PM +0530, Neeraj Upadhyay wrote: > If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall() > does checks to figure out whether jiffies is past rsp->jiffies_stall, > doing ordered accesses to avoid any false positives for new grace > period initialization after a sufficiently large idle period. This > extra processing can be skipped if rcu_cpu_stall_suppress is set. Just to make sure I understand, the concern is that someone might have booted with rcupdate.rcu_cpu_stall_suppress=1 (thus suppressing the RCU CPU stall debugging warnings implemented later in check_cpu_stall()), but later decided to also boot with rcutree.rcu_kick_kthreads=1 (thus enabling kicking kthreads which check for RCU's grace-period kthreads not being properly awakened)? My immediate reaction is that if there is not much point in specifying both rcutree.rcu_kick_kthreads=1 and rcupdate.rcu_cpu_stall_suppress=1. But is there some use case that I am missing? Thanx, Paul > Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS") > Signed-off-by: Neeraj Upadhyay > --- > kernel/rcu/tree.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 51d4c3a..91b7552 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) > unsigned long js; > struct rcu_node *rnp; > > - if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || > - !rcu_gp_in_progress(rsp)) > + if (!rcu_gp_in_progress(rsp)) > return; > rcu_stall_kick_kthreads(rsp); > + > + if (rcu_cpu_stall_suppress) > + return; > + > j = jiffies; > > /* > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation >