From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6DE86C742A7 for ; Sat, 13 Jul 2019 14:19:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4070220830 for ; Sat, 13 Jul 2019 14:19:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727626AbfGMOTg (ORCPT ); Sat, 13 Jul 2019 10:19:36 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:30726 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727504AbfGMOTg (ORCPT ); Sat, 13 Jul 2019 10:19:36 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x6DEHvId021437; Sat, 13 Jul 2019 10:18:54 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2tq86bm8ft-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sat, 13 Jul 2019 10:18:53 -0400 Received: from m0098393.ppops.net (m0098393.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x6DEIrwh023291; Sat, 13 Jul 2019 10:18:53 -0400 Received: from ppma01dal.us.ibm.com (83.d6.3fa9.ip4.static.sl-reverse.com [169.63.214.131]) by mx0a-001b2d01.pphosted.com with ESMTP id 2tq86bm8fk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sat, 13 Jul 2019 10:18:53 -0400 Received: from pps.filterd (ppma01dal.us.ibm.com [127.0.0.1]) by ppma01dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x6DEErnG020195; Sat, 13 Jul 2019 14:18:52 GMT Received: from b01cxnp23032.gho.pok.ibm.com (b01cxnp23032.gho.pok.ibm.com [9.57.198.27]) by ppma01dal.us.ibm.com with ESMTP id 2tq6x62vmk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sat, 13 Jul 2019 14:18:52 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x6DEIpjY46661898 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 13 Jul 2019 14:18:51 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 387EDB2065; Sat, 13 Jul 2019 14:18:51 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 00F2AB2064; Sat, 13 Jul 2019 14:18:50 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.158.189]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Sat, 13 Jul 2019 14:18:50 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id ABD1116C8E80; Sat, 13 Jul 2019 07:18:50 -0700 (PDT) Date: Sat, 13 Jul 2019 07:18:50 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Byungchul Park , linux-kernel@vger.kernel.org, Davidlohr Bueso , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt , kernel-team@android.com Subject: Re: [PATCH] rcuperf: Make rcuperf kernel test more robust for !expedited mode Message-ID: <20190713141850.GC26519@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190704043431.208689-1-joel@joelfernandes.org> <20190704174044.GK26519@linux.ibm.com> <20190705035231.GA31088@X58A-UD3R> <20190705122450.GA82532@google.com> <20190705150932.GO26519@linux.ibm.com> <20190705200003.GB134527@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190705200003.GB134527@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-13_03:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907130175 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Jul 05, 2019 at 04:00:03PM -0400, Joel Fernandes wrote: > On Fri, Jul 05, 2019 at 08:09:32AM -0700, Paul E. McKenney wrote: > > On Fri, Jul 05, 2019 at 08:24:50AM -0400, Joel Fernandes wrote: > > > On Fri, Jul 05, 2019 at 12:52:31PM +0900, Byungchul Park wrote: > > > > On Thu, Jul 04, 2019 at 10:40:44AM -0700, Paul E. McKenney wrote: > > > > > On Thu, Jul 04, 2019 at 12:34:30AM -0400, Joel Fernandes (Google) wrote: > > > > > > It is possible that the rcuperf kernel test runs concurrently with init > > > > > > starting up. During this time, the system is running all grace periods > > > > > > as expedited. However, rcuperf can also be run for normal GP tests. > > > > > > Right now, it depends on a holdoff time before starting the test to > > > > > > ensure grace periods start later. This works fine with the default > > > > > > holdoff time however it is not robust in situations where init takes > > > > > > greater than the holdoff time to finish running. Or, as in my case: > > > > > > > > > > > > I modified the rcuperf test locally to also run a thread that did > > > > > > preempt disable/enable in a loop. This had the effect of slowing down > > > > > > init. The end result was that the "batches:" counter in rcuperf was 0 > > > > > > causing a division by 0 error in the results. This counter was 0 because > > > > > > only expedited GPs seem to happen, not normal ones which led to the > > > > > > rcu_state.gp_seq counter remaining constant across grace periods which > > > > > > unexpectedly happen to be expedited. The system was running expedited > > > > > > RCU all the time because rcu_unexpedited_gp() would not have run yet > > > > > > from init. In other words, the test would concurrently with init > > > > > > booting in expedited GP mode. > > > > > > > > > > > > To fix this properly, let us check if system_state if SYSTEM_RUNNING > > > > > > is set before starting the test. The system_state approximately aligns > > > > > > > > Just minor typo.. > > > > > > > > To fix this properly, let us check if system_state if SYSTEM_RUNNING > > > > is set before starting the test. ... > > > > > > > > Should be > > > > > > > > To fix this properly, let us check if system_state is set to > > > > SYSTEM_RUNNING before starting the test. ... > > > > > > That's a fair point. I wonder if Paul already fixed it up in his tree, > > > however I am happy to resend if he hasn't. Paul, how would you like to handle > > > this commit log nit? > > > > > > it is just 'if ..' to 'is SYSTEM_RUNNING' > > > > It now reads as follows: > > > > To fix this properly, this commit waits until system_state is > > set to SYSTEM_RUNNING before starting the test. This change is > > made just before kernel_init() invokes rcu_end_inkernel_boot(), > > and this latter is what turns off boot-time expediting of RCU > > grace periods. > > Ok, looks good to me, thanks. > > And for below patch, > > Reviewed-by: Joel Fernandes (Google) Applied, thank you! Thnax, Paul > > I dropped the last paragraph about late_initcall(). And I suspect that > > the last clause from rcu_gp_is_expedited() can be dropped: > > > > bool rcu_gp_is_expedited(void) > > { > > return rcu_expedited || atomic_read(&rcu_expedited_nesting) || > > rcu_scheduler_active == RCU_SCHEDULER_INIT; > > } > > > > This is because rcu_expedited_nesting is initialized to 1, and is > > decremented in rcu_end_inkernel_boot(), which is called long after > > rcu_scheduler_active has been set to RCU_SCHEDULER_RUNNING, which > > happens at core_initcall() time. So if the last clause says "true", > > so does the second-to-last clause. > > > > The similar check in rcu_gp_is_normal() is still need, however, to allow > > the power-management subsystem to invoke synchronize_rcu() just after > > the scheduler has been initialized, but before RCU is aware of this. > > > > So, how about the commit shown below? > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit 1f7e72efe3c761c2b34da7b59e01ad69c657db10 > > Author: Paul E. McKenney > > Date: Fri Jul 5 08:05:10 2019 -0700 > > > > rcu: Remove redundant "if" condition from rcu_gp_is_expedited() > > > > Because rcu_expedited_nesting is initialized to 1 and not decremented > > until just before init is spawned, rcu_expedited_nesting is guaranteed > > to be non-zero whenever rcu_scheduler_active == RCU_SCHEDULER_INIT. > > This commit therefore removes this redundant "if" equality test. > > > > Signed-off-by: Paul E. McKenney > > > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > > index 249517058b13..64e9cc8609e7 100644 > > --- a/kernel/rcu/update.c > > +++ b/kernel/rcu/update.c > > @@ -136,8 +136,7 @@ static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); > > */ > > bool rcu_gp_is_expedited(void) > > { > > - return rcu_expedited || atomic_read(&rcu_expedited_nesting) || > > - rcu_scheduler_active == RCU_SCHEDULER_INIT; > > + return rcu_expedited || atomic_read(&rcu_expedited_nesting); > > } > > EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); > > > > >