From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 340887D910 for ; Fri, 30 Aug 2019 01:09:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727433AbfH3BJt (ORCPT ); Thu, 29 Aug 2019 21:09:49 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34516 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727066AbfH3BJt (ORCPT ); Thu, 29 Aug 2019 21:09:49 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x7U184vH045570; Thu, 29 Aug 2019 21:09:09 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2upp2demqv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Aug 2019 21:09:09 -0400 Received: from m0098410.ppops.net (m0098410.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x7U1970K048213; Thu, 29 Aug 2019 21:09:08 -0400 Received: from ppma05wdc.us.ibm.com (1b.90.2fa9.ip4.static.sl-reverse.com [169.47.144.27]) by mx0a-001b2d01.pphosted.com with ESMTP id 2upp2demqb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Aug 2019 21:09:08 -0400 Received: from pps.filterd (ppma05wdc.us.ibm.com [127.0.0.1]) by ppma05wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x7U17NHZ005547; Fri, 30 Aug 2019 01:09:07 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma05wdc.us.ibm.com with ESMTP id 2ujvv7fu61-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 30 Aug 2019 01:09:06 +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 x7U195ZN36438402 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 30 Aug 2019 01:09:05 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6DEA6B2065; Fri, 30 Aug 2019 01:09:05 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 579D3B206E; Fri, 30 Aug 2019 01:09:05 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.80.201.94]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 30 Aug 2019 01:09:05 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 6530216C1310; Thu, 29 Aug 2019 17:48:18 -0700 (PDT) Date: Thu, 29 Aug 2019 17:48:18 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Andy Lutomirski , LKML , Frederic Weisbecker , Jonathan Corbet , Josh Triplett , Android Kernel Team , Lai Jiangshan , "open list:DOCUMENTATION" , Mathieu Desnoyers , Mauro Carvalho Chehab , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [RFC v1 2/2] rcu/tree: Remove dynticks_nmi_nesting counter Message-ID: <20190830004818.GX4125@linux.ibm.com> Reply-To: paulmck@kernel.org References: <20190828220108.GC26530@linux.ibm.com> <20190828221444.GA100789@google.com> <20190828231247.GE26530@linux.ibm.com> <20190829015155.GB100789@google.com> <20190829034336.GD4125@linux.ibm.com> <20190829144355.GE63638@google.com> <20190829160946.GP4125@linux.ibm.com> <20190829165407.GT4125@linux.ibm.com> <20190829190046.GB115245@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190829190046.GB115245@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=2019-08-30_01:,, 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=1034 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=965 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908300009 Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Thu, Aug 29, 2019 at 03:00:46PM -0400, Joel Fernandes wrote: > Hi Paul, > > On Thu, Aug 29, 2019 at 09:54:07AM -0700, Paul E. McKenney wrote: > > On Thu, Aug 29, 2019 at 09:21:46AM -0700, Andy Lutomirski wrote: > > > On Thu, Aug 29, 2019 at 9:10 AM Paul E. McKenney wrote: > > > > > > > > On Thu, Aug 29, 2019 at 10:43:55AM -0400, Joel Fernandes wrote: > > > > > > > > [ . . . ] > > > > > > > > > Paul, do we also nuke rcu_eqs_special_set()? Currently I don't see anyone > > > > > using it. And also remove the bottom most bit of dynticks? > > > > > > > > > > Also what happens if a TLB flush broadcast is needed? Do we IPI nohz or idle > > > > > CPUs are the moment? > > > > > > > > > > All of this was introduced in: > > > > > b8c17e6664c4 ("rcu: Maintain special bits at bottom of ->dynticks counter") > > > > > > > > Adding Andy Lutomirski on CC. > > > > > > > > Andy, is this going to be used in the near term, or should we just get > > > > rid of it? > > > > > > Let's get rid of it. I'm not actually convinced it *can* be used as designed. > > > > > > For those who forgot the history or weren't cc'd on all of it: I had > > > this clever idea about how we could reduce TLB flushes. I implemented > > > some of it (but not the part that would have used this RCU feature), > > > and it exploded in nasty and subtle ways. This caused me to learn > > > that speculative TLB fills were a problem that I had entirely failed > > > to account for. Then PTI happened and thoroughly muddied the water. > > > > Yeah, PTI was quite annoying. Still is, from what I can see. :-/ > > > > > So I think we should just drop this :( > > > > OK, thank you! I will put a tag into -rcu marking its removal in case > > it should prove useful whenever for whatever. > > > > Joel, would you like to remove this, or would you rather that I did? > > It is in code you are working with right now, so if I do it, I need to > > wait until yours is finalized. Which wouldn't be a problem. > > I can remove it in my series, made a note to do so. Sounds good! Thanx, Paul