Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965168AbdDSPNm (ORCPT ); Wed, 19 Apr 2017 11:13:42 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45374 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965146AbdDSPNf (ORCPT ); Wed, 19 Apr 2017 11:13:35 -0400 Date: Wed, 19 Apr 2017 08:13:07 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Christian Borntraeger , 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, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, marc.zyngier@arm.com Subject: Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12 Reply-To: paulmck@linux.vnet.ibm.com References: <20170412165441.GA17149@linux.vnet.ibm.com> <20170417232714.GA19013@linux.vnet.ibm.com> <20170419112845.3rt3zlyzuzert647@hirez.programming.kicks-ass.net> <20170419120847.GB3029@worktop.programming.kicks-ass.net> <20170419144730.GA20845@linux.vnet.ibm.com> <20170419145214.y4in7mjfyhu33bpt@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170419145214.y4in7mjfyhu33bpt@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17041915-0048-0000-0000-000001618F2E X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006939; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00849647; UDB=6.00419562; IPR=6.00628281; BA=6.00005304; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015095; XFM=3.00000013; UTC=2017-04-19 15:13:28 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041915-0049-0000-0000-0000409F1145 Message-Id: <20170419151307.GN3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-19_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1704190128 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1014 Lines: 21 On Wed, Apr 19, 2017 at 04:52:15PM +0200, Peter Zijlstra wrote: > On Wed, Apr 19, 2017 at 07:47:30AM -0700, Paul E. McKenney wrote: > > The RCU expedited primitives have been completely rewritten since then, > > and no longer use try_stop_cpus(), no longer disturb idle CPUs, and no > > longer disturb nohz_full CPUs running in userspace. In addition, there > > is the rcupdate.rcu_normal kernel boot paramter for those who want to > > completely avoid RCU expedited primitives. > > > > So it seems to me to be time for the patch below. Thoughts? > > So I forgot all the details again; but if I'm not mistaken it still > prods CPUs with IPIs (just not idle/nohz_full CPUs). So its still not > ideal to sprinkle them around. > > Which would still argue against using them too much. True, but we have any number of things in the kernel that do IPIs, including simple wakeups. Adding checkpatch warnings for all of them seems silly, as does singling out only one of them. Hence the patch. Thanx, Paul