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 20CD97D2F0 for ; Thu, 29 Aug 2019 16:33:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726739AbfH2Qdd (ORCPT ); Thu, 29 Aug 2019 12:33:33 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:63426 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726973AbfH2Qdd (ORCPT ); Thu, 29 Aug 2019 12:33:33 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x7TGWriX025432; Thu, 29 Aug 2019 12:32:59 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2upfu0pqdg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Aug 2019 12:32:59 -0400 Received: from m0098396.ppops.net (m0098396.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x7TGWx6V025707; Thu, 29 Aug 2019 12:32:59 -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 2upfu0pqb7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Aug 2019 12:32:58 -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 x7TGUYSw018370; Thu, 29 Aug 2019 16:32:55 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma01dal.us.ibm.com with ESMTP id 2unb3t6rp5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 29 Aug 2019 16:32:55 +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 x7TGWsmi16122704 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 29 Aug 2019 16:32:54 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AA6F0B205F; Thu, 29 Aug 2019 16:32:54 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 873D7B2065; Thu, 29 Aug 2019 16:32:54 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.85.151.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 29 Aug 2019 16:32:54 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 2A82216C0C06; Thu, 29 Aug 2019 09:32:55 -0700 (PDT) Date: Thu, 29 Aug 2019 09:32:55 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Frederic Weisbecker , Jonathan Corbet , Josh Triplett , kernel-team@android.com, Lai Jiangshan , linux-doc@vger.kernel.org, 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: <20190829163255.GA15605@linux.ibm.com> Reply-To: paulmck@kernel.org References: <20190828202330.GS26530@linux.ibm.com> <20190828210525.GB75931@google.com> <20190828211904.GX26530@linux.ibm.com> <20190828214241.GD75931@google.com> <20190828220108.GC26530@linux.ibm.com> <20190828221444.GA100789@google.com> <20190828231247.GE26530@linux.ibm.com> <20190829015155.GB100789@google.com> <20190829034336.GD4125@linux.ibm.com> <20190829135907.GC63638@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190829135907.GC63638@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=2019-08-29_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=1034 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=847 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908290175 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 09:59:07AM -0400, Joel Fernandes wrote: > On Wed, Aug 28, 2019 at 08:43:36PM -0700, Paul E. McKenney wrote: > [snip] > > On the tracing patch... That patch might be a good idea regardless, > > but I bet that the reason that you felt the sudden need for it was due > > to the loss of information in your eventual ->dynticks_nesting field. > > After all, the value 0x1 might be an interrupt from idle, or it might > > just as easily be a task running in the kernel at process level. > > True, however what really triggered me to do it was the existing code which > does not distinguish between entry/exit from USER and IDLE. > > > The reason the patch might nevertheless be a good idea is that redundant > > information can be helpful when debugging. Especially when debugging > > new architecture-specific code, which is when RCU's dyntick-idle warnings > > tend to find bugs. > > Sure, and also that it is more readable to ordinary human beings than "++=" > and "--=" :-D. And those considerations did figure into my deciding that the tracing change was likely a good thing in any case. ;-) Thanx, Paul