From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751696AbdAPXsV (ORCPT ); Mon, 16 Jan 2017 18:48:21 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48640 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751156AbdAPXsU (ORCPT ); Mon, 16 Jan 2017 18:48:20 -0500 Date: Mon, 16 Jan 2017 15:48:13 -0800 From: "Paul E. McKenney" To: Josh Triplett Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks momentary-idle operation Reply-To: paulmck@linux.vnet.ibm.com References: <20170114085406.GA19052@linux.vnet.ibm.com> <1484384085-19444-1-git-send-email-paulmck@linux.vnet.ibm.com> <20170116073951.ipupoxcjnv42dwop@x> <20170116112239.GL5238@linux.vnet.ibm.com> <20170116185704.2cpgih6idiegn7k3@x> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170116185704.2cpgih6idiegn7k3@x> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17011623-0004-0000-0000-0000114D1DE7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006446; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000199; SDB=6.00808579; UDB=6.00393809; IPR=6.00585938; BA=6.00005062; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013943; XFM=3.00000011; UTC=2017-01-16 23:48:17 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17011623-0005-0000-0000-00007C37A6AF Message-Id: <20170116234813.GT5238@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-01-16_18:,, 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=8.0.1-1612050000 definitions=main-1701160329 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 16, 2017 at 10:57:04AM -0800, Josh Triplett wrote: > On Mon, Jan 16, 2017 at 03:22:39AM -0800, Paul E. McKenney wrote: > > On Sun, Jan 15, 2017 at 11:39:51PM -0800, Josh Triplett wrote: > > > On Sat, Jan 14, 2017 at 12:54:40AM -0800, Paul E. McKenney wrote: > > > > This commit is the first step towards full abstraction of all accesses to > > > > the ->dynticks counter, implementing the previously open-coded atomic add > > > > of two in a new rcu_dynticks_momentary_idle() function. This abstraction > > > > will ease changes to the ->dynticks counter operation. > > > > > > > > Signed-off-by: Paul E. McKenney > > > > > > This change has an additional effect not documented in the commit > > > message: it eliminates the smp_mb__before_atomic and > > > smp_mb__after_atomic calls. Can you please document that in the commit > > > message, and explain why that doesn't cause a problem? > > > > The trick is that the old code used the non-value-returning atomic_add(), > > which does not imply ordering, hence the smp_mb__before_atomic() and > > smp_mb__after_atomic() calls. The new code uses atomic_add_return(), > > which does return a value, and therefore implies full ordering in and > > of itself. > > > > How would you like me to proceed? > > With the above explanation added to the commit message: > > Reviewed-by: Josh Triplett Done, thank you! Thanx, Paul