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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 0DE4CC433FF for ; Mon, 5 Aug 2019 14:49:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D651220644 for ; Mon, 5 Aug 2019 14:49:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726508AbfHEOtB (ORCPT ); Mon, 5 Aug 2019 10:49:01 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:15926 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727357AbfHEOtB (ORCPT ); Mon, 5 Aug 2019 10:49:01 -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 x75Em1Xu120204; Mon, 5 Aug 2019 10:48:18 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2u6kyxg9mv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 05 Aug 2019 10:48:15 -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 x75Em55C120592; Mon, 5 Aug 2019 10:48:05 -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 2u6kyxg9ea-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 05 Aug 2019 10:48:05 -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 x75EjCZ7025725; Mon, 5 Aug 2019 14:47:53 GMT Received: from b01cxnp22035.gho.pok.ibm.com (b01cxnp22035.gho.pok.ibm.com [9.57.198.25]) by ppma01dal.us.ibm.com with ESMTP id 2u51w6sd0b-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 05 Aug 2019 14:47:53 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x75Elr0R50659622 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 5 Aug 2019 14:47:53 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E730CB205F; Mon, 5 Aug 2019 14:47:52 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C7D7AB2066; Mon, 5 Aug 2019 14:47:52 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 5 Aug 2019 14:47:52 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id E47F216C9A47; Mon, 5 Aug 2019 07:47:55 -0700 (PDT) Date: Mon, 5 Aug 2019 07:47:55 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: rcu@vger.kernel.org, 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@joelfernandes.org Subject: Re: [PATCH RFC tip/core/rcu 14/14] rcu/nohz: Make multi_cpu_stop() enable tick on all online CPUs Message-ID: <20190805144755.GH28441@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190802151435.GA1081@linux.ibm.com> <20190802151501.13069-14-paulmck@linux.ibm.com> <20190804144317.GF2349@hirez.programming.kicks-ass.net> <20190804144835.GB2386@hirez.programming.kicks-ass.net> <20190804184159.GC28441@linux.ibm.com> <20190804202446.GA25634@linux.ibm.com> <20190805041901.GA17621@linux.ibm.com> <20190805080736.GI2349@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190805080736.GI2349@hirez.programming.kicks-ass.net> 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=2019-08-05_07:,, 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=8.0.1-1906280000 definitions=main-1908050165 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Aug 05, 2019 at 10:07:36AM +0200, Peter Zijlstra wrote: > On Sun, Aug 04, 2019 at 09:19:01PM -0700, Paul E. McKenney wrote: > > On Sun, Aug 04, 2019 at 01:24:46PM -0700, Paul E. McKenney wrote: > > > > For whatever it is worth, the things on my list include using 25 rounds > > > of resched_cpu() on each CPU with ten-jiffy wait between each (instead of > > > merely 10 rounds), using waitqueues or some such to actually force a > > > meaningful context switch on the other CPUs, etc. > > That really should not be needed. What are those other CPUs doing? Excellent question. It would be really nice to have a CPU-stopper stall warning, wouldn't it? But who knows? Maybe I am the only one to have run into this. However, the comment in multi_cpu_stop() just before the call to touch_nmi_watchdog() leads me to believe otherwise. ;-) > > Which appears to have reduced the bug rate by about a factor of two. > > (But statistics and all that.) > > Which is just weird.. Indeed. Your point being? > > I am now trying the same test, but with CONFIG_PREEMPT=y and without > > quite so much hammering on the scheduler. This is keying off Peter's > > earlier mention of preemption. If this turns out to be solid, perhaps > > we outlaw CONFIG_PREEMPT=n && CONFIG_NO_HZ_FULL=y? > > CONFIG_PREEMPT=n should work just fine, _something_ is off. Thank you, that is what I needed to know. Thanx, Paul