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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 88B33C3A5A0 for ; Mon, 19 Aug 2019 14:41:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 64C7D206C1 for ; Mon, 19 Aug 2019 14:41:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726636AbfHSOlJ (ORCPT ); Mon, 19 Aug 2019 10:41:09 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:31742 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726211AbfHSOlJ (ORCPT ); Mon, 19 Aug 2019 10:41:09 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x7JEceEm163784; Mon, 19 Aug 2019 10:41:06 -0400 Received: from ppma03dal.us.ibm.com (b.bd.3ea9.ip4.static.sl-reverse.com [169.62.189.11]) by mx0b-001b2d01.pphosted.com with ESMTP id 2ufwbm920t-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 19 Aug 2019 10:41:05 -0400 Received: from pps.filterd (ppma03dal.us.ibm.com [127.0.0.1]) by ppma03dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x7JEdo6H022996; Mon, 19 Aug 2019 14:41:05 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma03dal.us.ibm.com with ESMTP id 2ue976egka-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 19 Aug 2019 14:41:04 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x7JEf4Q515139790 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 19 Aug 2019 14:41:04 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1CE1AB205F; Mon, 19 Aug 2019 14:41:04 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 00952B2066; Mon, 19 Aug 2019 14:41:03 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 19 Aug 2019 14:41:03 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 082CF16C17BA; Mon, 19 Aug 2019 07:41:08 -0700 (PDT) Date: Mon, 19 Aug 2019 07:41:08 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Frederic Weisbecker , linux-kernel@vger.kernel.org, rcu@vger.kernel.org Subject: Re: [PATCH -rcu dev 3/3] RFC: rcu/tree: Read dynticks_nmi_nesting in advance Message-ID: <20190819144107.GV28441@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190816025311.241257-1-joel@joelfernandes.org> <20190816025311.241257-3-joel@joelfernandes.org> <20190816162404.GB10481@google.com> <20190816165242.GS28441@linux.ibm.com> <20190819125907.GD27088@lenoir> <20190819142208.GA117378@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190819142208.GA117378@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=2019-08-19_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=8.0.1-1906280000 definitions=main-1908190165 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Aug 19, 2019 at 10:22:08AM -0400, Joel Fernandes wrote: > On Mon, Aug 19, 2019 at 02:59:08PM +0200, Frederic Weisbecker wrote: > > On Fri, Aug 16, 2019 at 09:52:42AM -0700, Paul E. McKenney wrote: > > > On Fri, Aug 16, 2019 at 12:24:04PM -0400, Joel Fernandes wrote: > > > > On Thu, Aug 15, 2019 at 10:53:11PM -0400, Joel Fernandes (Google) wrote: > > > > > I really cannot explain this patch, but without it, the "else if" block > > > > > just doesn't execute thus causing the tick's dep mask to not be set and > > > > > causes the tick to be turned off. > > > > > > > > > > I tried various _ONCE() macros but the only thing that works is this > > > > > patch. > > > > > > > > > > Signed-off-by: Joel Fernandes (Google) > > > > > --- > > > > > kernel/rcu/tree.c | 3 ++- > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > index 856d3c9f1955..ac6bcf7614d7 100644 > > > > > --- a/kernel/rcu/tree.c > > > > > +++ b/kernel/rcu/tree.c > > > > > @@ -802,6 +802,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) > > > > > { > > > > > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > > > > long incby = 2; > > > > > + int dnn = rdp->dynticks_nmi_nesting; > > > > > > > > I believe the accidental sign extension / conversion from long to int was > > > > giving me an illusion since things started working well. Changing the 'int > > > > dnn' to 'long dnn' gives similar behavior as without this patch! At least I > > > > know now. Please feel free to ignore this particular RFC patch while I debug > > > > this more (over the weekend or early next week). The first 2 patches are > > > > good, just ignore this one. > > > > > > Ah, good point on the type! So you were ending up with zero due to the > > > low-order 32 bits of DYNTICK_IRQ_NONIDLE being zero, correct? If so, > > > the "!rdp->dynticks_nmi_nesting" instead needs to be something like > > > "rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE", which sounds like > > > it is actually worse then the earlier comparison against the constant 2. > > > > > > Sounds like I should revert the -rcu commit 805a16eaefc3 ("rcu: Force > > > nohz_full tick on upon irq enter instead of exit"). > > > > I can't find that patch so all I can say so far is that its title doesn't > > inspire me much. Do you still need that change for some reason? > > No we don't need it. Paul's dev branch fixed it by checking DYNTICK_IRQ_NONIDLE: > https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=227482fd4f3ede0502b586da28a59971dfbac0b0 Ah, so you have tested reverting this? If so, thank you very much! Thanx, Paul